                   FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                     No. 05-50401
                Plaintiff-Appellee,
               v.                               D.C. No.
                                              CR-03-00072-DT
KEVIN FREEMAN,
                                                 OPINION
             Defendant-Appellant.
                                         
        Appeal from the United States District Court
            for the Central District of California
       Dickran M. Tevrizian, District Judge, Presiding

                   Argued and Submitted
           October 18, 2006—Pasadena, California

                      Filed June 11, 2007

     Before: John R. Gibson,* Raymond C. Fisher, and
           Consuelo M. Callahan, Circuit Judges.

              Opinion by Judge John R. Gibson




  *The Honorable John R. Gibson, Senior Circuit Judge, United States
Court of Appeals for the Eighth Circuit, sitting by designation.

                               7071
                  UNITED STATES v. FREEMAN                7075


                         COUNSEL

Myra D. Mossman (argued), Santa Barbara, California, for the
defendant-appellant.

Debra Wong Yang, United States Attorney, Thomas P.
O’Brien, Assistant United States Attorney, Chief, Criminal
Division, Mark A. Young, Assistant United States Attorney,
Narcotics Section, Elana Artson (argued), Assistant United
States Attorney, Los Angeles, California, for the plaintiff-
appellee.


                         OPINION

JOHN R. GIBSON, Senior Circuit Judge:

   Kevin Freeman appeals from his conviction and sentence
on one count of conspiracy to manufacture and distribute at
least fifty grams of cocaine base and conspiracy to possess
with intent to distribute at least five hundred grams of
cocaine. Freeman argues that the district court erred in allow-
ing the government’s expert witness to testify regarding the
meaning of encoded drug language and to testify as a lay wit-
ness. Although portions of the expert witness’s testimony
7076              UNITED STATES v. FREEMAN
should have been excluded, we hold that the district court’s
error was harmless. Freeman’s additional claims are without
merit. We affirm.

                       I.   Background

   Kevin Freeman was the only defendant named in a three-
count indictment. Count One charged him with conspiracy to
manufacture and distribute at least fifty grams of cocaine base
as well as conspiracy to possess with intent to distribute at
least five hundred grams of cocaine in violation of 21 U.S.C.
§ 846. The other counts accused Freeman of manufacturing
and distributing cocaine base.

   The indictment alleged that as a part of the drug conspir-
acy, Freeman purchased cocaine from Corey Mitchell and
Maurice Brown. Mitchell and Brown were part of an earlier
twenty-three defendant indictment, and since that time Mitch-
ell had been cooperating with investigators. Freeman alleg-
edly converted the cocaine into cocaine base and returned the
cocaine to Brown for distribution in the Venice, California
area. The Drug Enforcement Administration (DEA) had been
investigating Mitchell and Brown as part of the Corey Mitch-
ell drug trafficking organization since January of 2001, and
during their investigation they intercepted telephone calls
between Freeman and Brown. The indictment detailed a series
of these calls between Freeman and Brown that occurred in
May and June of 2001 that, allegedly using coded language,
arranged for various drug transactions between Freeman,
Brown, and Mitchell.

   The evidence offered by the government at Freeman’s jury
trial consisted in large part of testimony from Bob Shin, a
detective for the Los Angeles Police Department who was
working with the DEA as a federal task force officer at the
time of the investigation. Detective Shin testified as to the
meaning of allegedly coded words used by Freeman in the
intercepted telephone calls to facilitate drug transactions.
                   UNITED STATES v. FREEMAN                  7077
Although none of the telephone calls contained explicit refer-
ences to cocaine, Shin testified that they concerned that sub-
ject. While some of Shin’s testimony focused on interpreting
words or phrases he was previously aware of, such as “iggi-
dy” or “all gravy,” other portions of Shin’s testimony focused
on interpreting both words that he was not familiar with
before the investigation and entire conversations. Defense
counsel objected to Shin’s interpretive testimony as hearsay,
speculation, and lacking foundation, an objection the court
overruled.

   The jury also heard testimony from Corey Mitchell. Mitch-
ell testified that he had been a drug trafficker for approxi-
mately ten years and had been selling drugs to Freeman for
approximately eight years. Mitchell testified that he originally
sold Freeman cocaine base but that Freeman began purchas-
ing powder cocaine sometime around 2000 because Freeman
had learned to “cook” powder cocaine into crack cocaine.
Mitchell described transactions involving Freeman cooking
cocaine for the purpose of giving half back to Mitchell and
Brown and keeping half to sell. Freeman also testified at trial.
He admitted that while he and Brown were friends, the con-
versations recorded by investigators did not involve drug
transactions, but rather the sale of stolen basketball tickets.

   The jury deliberated for portions of two days before
informing the district court that it was unable to reach a unan-
imous verdict. After learning that the jury had taken six bal-
lots, the judge decided to give the jury the following
instruction:

       Members of the Jury, you have advised that you
    have been unable to agree upon a verdict in this case.
    I’ve decided to suggest a few thoughts to you.

      As Jurors, you have a duty to discuss the case with
    one another and to deliberate in an effort to reach a
    unanimous verdict if each of you can do so without
7078              UNITED STATES v. FREEMAN
    violating your individual judgment and conscious
    [sic].

       Each of you must decide the case for yourself.
    But, only after you consider the evidence impartially
    with your fellow Jurors. During your deliberations,
    you should not hesitate to re-examine your own
    views and change your opinion if you become per-
    suaded that it is wrong.

       However, you should not change an honest belief
    as to the weight or effect of the evidence solely
    because of the opinions of your fellow Jurors or for
    the mere purpose of returning a verdict.

       All of you are equally honest and conscientious
    Jurors who have heard the same evidence. All of you
    share an equal desire to arrive at a verdict. Each of
    you should ask yourself whether you should question
    the correctness of your present position.

       I remind you that in your deliberations, you are to
    consider the instructions I have given you as a
    whole. You should not single out any part of any
    instruction, including this one and ignore others.
    They are equally important.

       You may now retire and continue your delibera-
    tions.

Two hours later, the jury returned verdicts of guilty on the
first count of the indictment and not guilty on the second and
third counts of the indictment.

   The district court denied Freeman’s motion for a new trial
and sentenced him to a term of 240 months imprisonment,
five years of supervised release, and a $100 special assess-
ment. Freeman now brings the present appeal.
                       UNITED STATES v. FREEMAN               7079
                 II.     Agent Shin’s Testimony

   Freeman argues that the district court abused its discretion
by allowing Shin to testify as to the meaning of coded drug
language used in telephone conversations between Freeman,
Mitchell, and Brown. Shin investigated the Corey Mitchell
drug trafficking organization from February of 2001 through
the time of Freeman’s arrest. He was one of only four prose-
cution witnesses, and his testimony spanned three of the four
days during which the prosecution presented its case. Shin
offered interpretations regarding the meaning of thirty-six
recorded telephone calls. Several of the words he interpreted
were part of the jargon commonly used by drug traffickers
and were familiar to Shin before the investigation. For
instance, he testified that “ticket” signifies a drug price; “iggi-
dy” refers to an ounce; “all gravy” and “straight” both signify
that the situation is good; “dove” refers to the number twenty;
and the terms “bread,” “cheese,” and “chips” all refer to
money.

   Shin also interpreted a number of words that he was not
familiar with before the investigation but, as he explained, are
easily decoded based on a manner of speaking common to
drug traffickers. Shin testified that Freeman, Brown, and
Mitchell altered words by placing “e-z” or some variant
thereof in the middle of words. He interpreted “fezone” to
mean phone; “teznower” to mean tower; “fezo” to signify
four and “fezi” to signify five; “deezove” to mean dove; “pee-
zark” to mean park; and “reezey” to mean ready.

   Shin also offered interpretations for drug jargon that he was
not familiar with before the investigation, but was able to
decipher on the basis of the investigation and his general
experience with drug trafficking. For example, Shin explained
on the basis of his knowledge of the street value of cocaine
that “cuatro-cinco,” which are the Spanish words for four and
five, signified $450. “Piece,” according to Shin, signified
ounce, and it was a term that he was able to decipher based
7080               UNITED STATES v. FREEMAN
on the context of a conversation between Mitchell and Brown.
Shin interpreted “diamond” to signify the ten ounces of crack
that would be produced by cooking nine ounces of powder
cocaine. In this instance, Brown helped to reveal the term’s
meaning by stating that he was going to “pull ten,” and then
correcting himself by stating that he would pull a “diamond.”
Shin explained that he was familiar with the process of con-
verting powder cocaine into crack cocaine, and that with skill,
an individual is able to increase the total weight of drugs.

   Shin also offered explanations of statements by Freeman,
Brown, and Mitchell that were not encoded drug jargon, but
instead were phrases that were more likely to be understood
by the jurors without assistance. When Brown instructed
Mitchell to speak with him later so that they “can get all the
particulars,” Shin stated that “particulars” was a reference to
the “details.” Shin explained that when Mitchell asked Brown
during one recorded call how everything had turned out, this
signified that Mitchell was asking Brown how did the “drug
deal turn out, how did everything go?”

   There were other phrases that Shin interpreted that were not
encoded drug language, but rather ambiguous statements con-
sisting of ordinary terms. For one recorded conversation, Shin
interpreted “long route” to mean a specific method for com-
pleting the drug transaction; “that” to signify money; and,
later in the conversation, “that” to signify cocaine. In many
instances, Shin was careful to explain his reasoning and the
basis for his opinion. He offered his opinion as to the meaning
of several conversations on the basis of context and his
knowledge of the investigation as it was unfolding. At other
points, however, Shin did not give an explanation of his rea-
soning. For example, during one recorded telephone call,
Mitchell stated that he “touched bases with two of those.”
Shin testified, without offering an explanation, that this meant
that Mitchell was able to obtain two kilograms of cocaine.
During another recorded telephone call, Freeman informed
Brown that he wished to get off of the telephone while driv-
                       UNITED STATES v. FREEMAN                        7081
ing. When questioned by the prosecutor about this, Shin testi-
fied that Freeman’s desire to get off of the telephone was
motivated by a fear of being pulled over and arrested for the
possession of cocaine. Shin opined that during the telephone
call, Freeman “wants to drive carefully so that he doesn’t
make any mistakes driving . . . or break any traffic laws where
he’s pulled over by law enforcement . . . and then searched,
which possibly could lead to the search and discovery” of
cocaine. Again, Shin offered no explanation for why this was
his interpretation, other than his belief that Freeman was car-
rying drugs.

  A.    Standard of Review

   On appeal, Freeman argues that the district court commit-
ted error by allowing Shin to testify both as a lay witness as
well as an expert witness and that the district court never
properly admitted Shin as an expert witness.1 Freeman further
contends that the district court, by permitting Shin to testify
as a fact witness, circumvented Fed. R. Evid. 702 and allowed
Shin to testify in an unreliable manner. Freeman also argues
that Shin was allowed to offer an opinion regarding ultimate
factual issues, in violation of Fed. R. Evid. 704(b). The dis-
trict court’s decision to admit expert testimony is reviewed for
abuse of discretion. United States v. Alatorre, 222 F.3d 1098,
1100 (9th Cir. 2000). We analyze Freeman’s arguments under
   1
     Regarding Shin testifying as an expert, we find no error by the district
court. At the time of trial, Shin had been a police officer for eleven years,
with more than four years of experience as a narcotics detective. Shin also
testified that at the time of trial, he had participated in over one hundred
narcotics investigations. Based upon his experience, Shin was qualified to
offer expert testimony regarding the meaning of encoded drug jargon.
Shin’s expert testimony was also adequately disclosed under Fed. R. Crim.
P. 16, and thus the testimony was properly admitted.
   Freeman also argues that the district court improperly allowed Mitchell
to testify regarding coded drug language. However, as a participant in the
conspiracy, Mitchell could testify regarding his understanding of the
coded terms he and his coconspirators used.
7082               UNITED STATES v. FREEMAN
the harmless error standard used for reviewing non-
constitutional evidentiary rulings: We are compelled to
reverse the conviction “unless it is more probable than not
that the error did not materially affect the verdict.” United
States v. Morales, 108 F.3d 1031, 1040 (9th Cir. 1997).

  B.   Reliability of Agent Shin’s Testimony

   [1] The Supreme Court has established that Federal Rule of
Evidence 702 charges trial judges with the task of ensuring
“that any and all scientific testimony or evidence admitted is
not only relevant, but reliable.” Daubert v. Merrell Dow
Pharm., Inc., 509 U.S. 579, 589 (1993). The gatekeeping role
exercised by district courts “entails a preliminary assessment
of whether the reasoning or methodology underlying the testi-
mony is . . . valid and of whether that reasoning or methodol-
ogy properly can be applied to the facts in issue.” Id. at 592-
93. This role applies to all expert testimony, not only to “sci-
entific” expert testimony. Kumho Tire Co., Ltd. v. Carmich-
ael, 526 U.S. 137, 147 (1999).

   [2] Freeman contends that the district court erred in admit-
ting Shin’s testimony because the government failed to estab-
lish that Shin employed a reliable methodology in interpreting
encoded drug jargon. Drug jargon “is a specialized body of
knowledge, familiar only to those wise in the ways of the drug
trade, and therefore a fit subject for expert testimony.” United
States v. Griffith, 118 F.3d 318, 321 (5th Cir. 1997). As the
advisory committee notes to Rule 702 explain, such expert
testimony is admissible provided that “the principles and
methods [used by the expert] are reliable and applied reliably
to the facts of the case.” Fed. R. Evid. 702 advisory commit-
tee’s notes (2000 amendments).

   In support of his argument, Freeman relies on our decision
in United States v. Hermanek, 289 F.3d 1076 (9th Cir. 2002).
In Hermanek, the defendants appealed a district court’s deci-
sion to allow the government’s expert to interpret words and
                   UNITED STATES v. FREEMAN                 7083
phrases solely on the basis of the expert’s “general qualifica-
tions without requiring the government to explain the method
[the expert] used to arrive at his interpretations.” Id. at 1094.
Although the government made an adequate showing of the
witness’s experience, the witness did not explain in detail the
methods he used to arrive at his interpretations of words that
he was not familiar with before the investigation. The court
determined that there was “simply too great an analytical gap
between the data and the opinion proffered.” Id. at 1095
(quoting Gen. Elec. Co. v. Joiner, 522 U.S. 136, 146 (1997)).
The court noted, however, that it was “not hold[ing] that a
government expert . . . can never be qualified to interpret
coded drug conversations using words and phrases experi-
enced for the first time in the prosecution at issue,” because
such testimony would be admissible if the witness explained
the methodology used to arrive at specific interpretations. Id.
at 1096.

   [3] Our review of the record leads us to conclude that
Shin’s interpretation of encoded drug jargon was admissible.
Several terms, such as “iggidy,” “ticket,” and “all gravy” were
familiar to Shin before the investigation. Other terms, such as
“cuatro-cinco” and “diamond” were unfamiliar to Shin before
the investigation, but Shin explained during his testimony
how he arrived at his interpretations. Shin also offered inter-
pretations of altered words such as “fezone” and “teznower,”
which we have acknowledged uses a methodology that satis-
fies Hermanek. See United States v. Decoud, 456 F.3d 996,
1014 & n.6 (9th Cir. 2006). The district court therefore did
not err in allowing Shin to testify as to the meaning of
encoded drug jargon.

   [4] Shin’s testimony, however, touched on matters far
afield from the interpretation of encoded drug jargon when he
offered interpretations of ambiguous conversations that did
not consist of coded terms at all. For example, in one tele-
phone conversation between Brown and Mitchell, Shin inter-
preted “long route” to refer to a drug transaction. In several
7084               UNITED STATES v. FREEMAN
conversations, Shin interpreted ambiguous phrases such as
“that,” “they,” and “one of them,” to refer to either money or
cocaine. In another conversation, Shin interpreted Brown’s
statement, “Man, it’s done already” to mean “he’s given the
cocaine to Kevin Freeman and that he’s received his money
for it.” In these and other instances, Shin did nothing more
than offer one possible framework for understanding the con-
versation. When offering this type of testimony, Shin usually
explained his reasoning.

   [5] However, in these instances Shin ceased to apply his
specialized knowledge of drug jargon and the drug trade and
began to interpret ambiguous statements based on his general
knowledge of the investigation. He was therefore no longer
testifying as an expert but rather as a lay witness. See Fed. R.
Evid. 702 (stating that an expert opinion is based on “scien-
tific, technical or other specialized knowledge”); see also
Daubert, 509 U.S. at 589-91; Kumho Tire, 526 U.S. at 147-
48. A lay witness may provide opinion testimony regarding
the meaning of vague or ambiguous statements. See United
States v. Simas, 937 F.2d 459, 464-65 (9th Cir. 1991); United
States v. De Peri, 778 F.2d 963, 977-78 (3d Cir. 1985). But,
unlike expert testimony, lay opinion must be “rationally based
on the perception of the witness.” Fed. R. Evid. 701. It must
also be helpful to the jury in acquiring a “clear understanding
of the witness’s testimony or the determination of a fact in
issue.” Id. We have previously held these requirements were
met when a law enforcement investigator testified regarding
his understanding of the meaning of a declarant’s vague or
ambiguous statements. See Simas, 937 F.2d at 465
(“[Appellant’s] statements to the FBI agents were vague and,
at times, seemingly incomprehensible. The listener’s under-
standing of the words and innuendo was helpful to the jury in
determining what [the appellant] meant to convey.”); see also
De Peri, 778 F.2d at 977-78 (holding that it was permissible
for a lay witness to testify to his understanding of defendant’s
ambiguous references and unfinished sentences).
                   UNITED STATES v. FREEMAN                7085
   Freeman argues that it was error for the district court to
allow Shin to testify both as an expert witness concerning
coded drug terms and as a lay witness. The dangers high-
lighted by Freeman were analyzed in United States v. Dukag-
jini, 326 F.3d 45 (2d Cir. 2003). In that case an agent with the
DEA testified as an expert witness in the area of decoding
drug jargon and as a lay witness giving general explanations
of conversations between the targets of the investigation. See
id. at 49-51. The appellants argued that the government wit-
ness’s “dual roles as case agent and expert witness allowed
him to serve as a summary witness, improperly testifying as
an expert about the general meaning of conversations and the
facts of the case.” Id. at 53.

   [6] Dukagjini identified several difficulties that arise when
a case agent goes beyond interpreting code words as an expert
and testifies as to the defendant’s conduct based upon the
agent’s knowledge of the case. First, “by qualifying as an
‘expert,’ the witness attains unmerited credibility when testi-
fying about factual matters from first-hand knowledge.” Id.
Second, it is possible that “expert testimony by a fact witness
or case agent can inhibit cross-examination . . . [because a]
failed effort to impeach the witness as expert may effectively
enhance his credibility as a fact witness.” Id. at 53-54. Third,
“when the prosecution uses a case agent as an expert, there is
an increased danger that the expert testimony will stray from
applying reliable methodology and convey to the jury the wit-
ness’s ‘sweeping conclusions’ about appellants’ activities,
deviating from the strictures of Rules 403 and 702.” Id. at 54
(quoting United States v. Simmons, 923 F.2d 934, 946-947 n.5
(2d Cir. 1991). Fourth, a case agent testifying as an expert
may lead to juror confusion because “[s]ome jurors will find
it difficult to discern whether the witness is relying properly
on his general experience and reliable methodology, or
improperly on what he has learned of the case.” Id. Finally,
“when a case agent/expert strays from the scope of his exper-
tise, he may impermissibly rely upon and convey hearsay evi-
dence.” Id. at 55. In doing so, the witness may also run afoul
7086                 UNITED STATES v. FREEMAN
of the Sixth Amendment Confrontation Clause. See id. at 58-
59.2

   [7] We share the concerns expressed by the Second Circuit
in Dukagjini. First, we are concerned that a case agent who
testifies as an expert receives “unmerited credibility” for lay
testimony. Id. at 53. See Jinro America Inc. v. Secure Invest-
ments, Inc., 266 F.3d 993, 1004 (9th Cir. 2001) (noting that
because expert testimony is “likely to carry special weight
with the jury . . . care must be taken to assure that a proffered
witness truly qualifies as an expert”); United States v. Foster,
939 F.2d 445, 452 (7th Cir. 1991) (when expert witness also
serves as an eyewitness, district court and the prosecutor
should be vigilant in ensuring that “the jury understands its
function in evaluating the evidence and is not confused by the
witness’s dual role”); see also United States v. Alvarez, 837
F.2d 1024, 1030 (11th Cir. 1988) (when a government law
enforcement agent testifies as an expert, there is a risk that the
jury will give “undue weight” to the expert’s testimony). In
this case, the line between Shin’s lay and expert testimony
was never articulated for the jury. This lack of clarity regard-
ing Shin’s dual roles created a risk that there was an imprima-
tur of scientific or technical validity to the entirety of his
testimony.

   Second, we are also concerned that Shin was called upon
by the government to give his opinion as to the meaning of
numerous words and conversations, regardless of whether his
testimony, at points, was speculative or unnecessarily repeti-
tive. As Dukagjini explains, this form of expert testimony,
“unless closely monitored by the district court, may unfairly
provid[e] the government with an additional summation by
having the expert interpret the evidence, and may come dan-
gerously close to usurping the jury’s function. . . . Such sum-
  2
    Freeman did not raise a Confrontation Clause claim below and he does
not seek reversal on that basis here. Accordingly, we do not reach that
issue.
                   UNITED STATES v. FREEMAN                 7087
marizing also implicates Rule 403 as a needless presentation
of cumulative evidence and a waste of time.” 326 F.3d at 54
(citations and internal quotation marks omitted). See also
United States v. de Soto, 885 F.2d 354, 361 (7th Cir. 1989)
(when an expert testifies as to the meaning of seemingly
innocuous activities, district court ought be careful to ensure
that “the expert . . . not base his opinion on mere specula-
tion”). District courts have the continuing responsibility of
acting as the vigilant gatekeepers of expert testimony to
ensure that it is reliable. See Kumho, 526 U.S. at 147-149. The
fact that Shin possessed specialized knowledge of the particu-
lar language of drug traffickers did not give him carte blanche
to testify as to the meaning of other words in recorded tele-
phone calls without regard to reliability or relevance.

   Third, as noted, the blurred distinction between Shin’s
expert and lay testimony may have allowed him to rely upon
and convey inadmissible hearsay evidence. Once Shin
stopped testifying as an expert and began providing lay testi-
mony, he was no longer “allowed . . . to testify based on hear-
say information, and to couch his observations as generalized
‘opinions’ rather than as firsthand knowledge.” Jinro Amer-
ica, 266 F.3d at 1004; Cree v. Flores, 157 F.3d 762, 773 (9th
Cir. 1998) (noting that expert testimony is “not subject to the
strictures of Federal Rules of Evidence 602 and 803”). If Shin
relied upon or conveyed hearsay evidence when testifying as
a lay witness or if Shin based his lay testimony on matters not
within his personal knowledge, he exceeded the bounds of
properly admissible testimony.

   [8] We agree, however, that the use of case agents as both
expert and lay witnesses is not so inherently suspect that it
should be categorically prohibited. See Dukagjini, 326 F.3d at
56. Testimony of this kind may save time and expense, and
will not necessarily result in juror confusion, provided that the
district court engages in vigilant gatekeeping. We think that
it is sufficient to emphasize the necessity of making clear to
the jury what the attendant circumstances are in allowing a
7088               UNITED STATES v. FREEMAN
government case agent to testify as an expert. If jurors are
aware of the witness’s dual roles, the risk of error in these
types of trials is reduced.

   [9] Turning to the case at hand, Freeman failed to ask the
district court to instruct the jury regarding Shin’s dual role
and did not enter an objection raising that concern, such as an
objection based on Fed. R. Evid. 403. See Dukagjini, 326 F.3d
at 54 (noting that when an expert witness provides lay testi-
mony it implicates the concern under Rule 403 of juror confu-
sion). We therefore review Shin’s dual role testimony for
plain error. Because the distinction between lay and expert
testimony in this context is a fine one, we do not fault the dis-
trict court for failing to intervene sua sponte. Thus there was
no plain error. We also note that the opportunity does not lie
solely with the district court to clarify in the eyes of the jury
the demarcation between lay and expert testimony offered by
the same witness. That distinction can also be revealed
through direct or cross examination.

   Freeman did enter running objections to all of Shin’s testi-
mony based on hearsay, speculation, and lack of foundation.
Though Freeman did not specifically raise our concerns
regarding Shin’s testifying as a lay witness based on improper
grounds, his objections did raise the essence of these concerns
and we therefore do not review them for plain error but
instead apply the ordinary abuse of discretion standard. See
Decoud, 456 F.3d at 1010.

   [10] The record reveals that the majority of Shin’s lay testi-
mony consisted of his interpretations of ambiguous conversa-
tions based upon his direct knowledge of the entire
investigation. Although, unlike the witnesses in Simas and De
Peri, Shin was not a participant in the conversations he inter-
preted, his understanding of ambiguous phrases was based on
his direct perception of several hours of intercepted
conversations—in some instances coupled with direct obser-
vation of Freeman, Mitchell, and Brown—and other facts he
                   UNITED STATES v. FREEMAN                7089
learned during the investigation. See Simas, 937 F.2d at 464-
65 (noting that the perception of the witness requirement is
“simply a restatement of the personal knowledge requirement
for all lay testimony”); see also United States v. Beck, 418
F.3d 1008, 1015 (9th Cir. 2005) (holding that a lay witness’s
testimony is rationally based on the witness’s perceptions if
it is “based upon personal observation and recollection of
concrete facts”). Such testimony also proved helpful to the
jury in determining what Freeman, Mitchell, and Brown were
communicating during the recorded telephone calls.

   [11] Although Shin’s interpretation of ambiguous state-
ments was permissible under Fed. R. Evid. 701, “the interpre-
tation of clear statements is not permissible, and is barred by
the helpfulness requirement of both Fed. R. Evid. 701 and
Fed. R. Evid. 702.” United States v. Dicker, 853 F.2d 1103,
1109 (3d Cir. 1988) (emphasis in original); see also Scott v.
Sears, Roebuck & Co., 789 F.2d 1052, 1055 (4th Cir. 1986)
(noting that Rule 702 “makes inadmissible expert testimony
as to a matter which obviously is within the common knowl-
edge of jurors because such testimony, almost by definition,
can be of no assistance”). It is necessary that a lay witness’s
“opinions are based upon . . . direct perception of the event,
are not speculative, and are helpful to the determination” of
factual issues before the jury. De Peri, 778 F.2d at 977. Some
of Shin’s testimony, however, consisted of either speculation
or repetition of already clear statements. For example, Shin’s
unnecessary interpretation of “particulars” to signify “details”
was not helpful to the jury, thereby violating Rule 701. As
well, Shin’s opinion as to the reason why Freeman wished to
get off of the telephone while driving was speculation and
therefore was erroneously admitted.

   [12] Similarly, although Shin’s lay testimony for the most
part did not rely on or convey hearsay evidence, there were
a few exceptions. For example, Shin interpreted Freeman’s
statement in one call to Brown that “I’m going to bring that
to you at 1:00 tomorrow” to mean that Freeman would bring
7090              UNITED STATES v. FREEMAN
money to Brown that Freeman owed to Mitchell. Shin testi-
fied that his conclusion was based in part on interviews with
Mitchell, who had told investigators that Freeman owed
Brown money for cocaine that had been delivered before the
call. Because Shin was testifying as a lay witness in this
regard, his discussion of Mitchell’s hearsay statements should
not have been admitted.

  C.   Harmless Error

   [13] Having concluded that limited portions of Shin’s testi-
mony were erroneously admitted, we must now determine
whether the error was harmless. For errors that are not of con-
stitutional magnitude, the government must show that the
prejudice resulting from the error was more probably harm-
less than not. United States v. Mett, 178 F.3d 1058, 1066 (9th
Cir. 1999). This requires a “fair assurance” that the jury was
not substantially swayed by the error. Id. We conclude that
the errors we have highlighted, when viewed in the context of
the entirety of Shin’s testimony and other evidence offered by
the government, were harmless. As the district court con-
cluded:

    These telephone calls, which were interpreted by an
    experienced narcotics agent, established that defen-
    dant’s role in the conspiracy was to manufacture
    cocaine base from cocaine, and then distribute the
    cocaine base. In addition, these telephone calls and
    the government’s interpretation of these calls, were
    corroborated by surveillance of Brown and Mitchell
    preparing to conduct a drug transaction with defen-
    dant, and with the testimony of Mitchell. During
    trial, Mitchell testified that defendant had converted
    one kilogram of cocaine into cocaine base as part of
    the drug conspiracy.

Most of Agent Shin’s testimony focused on either interpreting
encoded drug jargon or permissibly interpreting ambiguous
                   UNITED STATES v. FREEMAN                7091
statements. Shin’s interpretations of the recorded conversa-
tions were often corroborated by the extensive surveillance he
and other investigators conducted during the course of the
investigation. For example, during one telephone call between
Mitchell and Brown, Shin was able to interpret a series of
words, including “chips,” “cheese,” “fezone,” “teznower,”
and “Cuz.” In that conversation, Shin interpreted Brown’s ref-
erence to “Cuz” to mean Freeman, and his interpretation was
corroborated by the fact that Brown’s next telephone call was
to Freeman. Likewise, Shin’s interpretation of “Teznower” to
reference Tower Records was corroborated by surveillance of
a meeting later that day between Brown and Mitchell at a
Tower Records in Marina Del Ray. Surveillance by the inves-
tigators, combined with Shin’s experience with encoded drug
jargon and his knowledge of the circumstances surrounding
the case, ensured a high degree of reliability for a majority of
Agent Shin’s testimony. The overwhelming portion of Shin’s
testimony was therefore properly admitted. This testimony
connected Freeman to illegal drug transactions and contra-
dicted his claim that the phone conversations concerned bas-
ketball tickets. In light of the evidence as a whole, we
conclude that the erroneously admitted testimony was harm-
less.

  D.   Rule 704(b)

   Freeman also argues that Shin offered opinions regarding
ultimate factual issues in violation of Fed. R. Evid. 704(b),
which provides that an expert witness may not state an opin-
ion as to whether the defendant did or did not have the mental
state or condition constituting an element of the crime or a
defense thereto. An expert witness is not permitted to offer a
direct opinion on the defendant’s guilt or innocence. See
United States v. Fleishman, 684 F.2d 1329, 1335-36 (9th Cir.
1982) (recognizing that there is a distinction between opinions
of guilt or innocence and “expert testimony regarding the var-
ious roles played by persons involved in illegal enterprises”).
According to Freeman, Shin violated Rule 704(b) by describ-
7092               UNITED STATES v. FREEMAN
ing drug traffickers’ general practice of encoding conversa-
tions so as to hide the fact that they are engaged in illegal
activity. Freeman’s argument is without merit.

   Government experts may “testify as to the general practices
of criminals to establish the defendants’ modus operandi”
which “helps the jury to understand complex criminal activi-
ties, and alerts it to the possibility that combinations of seem-
ingly innocuous events may indicate criminal behavior.”
United States v. Valencia Amezcua, 278 F.3d 901, 908-09 (9th
Cir. 2002) (quoting United States v. Johnson, 735 F.2d 1200,
1202 (9th Cir. 1984)). We have allowed modus operandi testi-
mony that “drug traffickers often employ counter-surveillance
driving techniques, register cars in others’ names, make nar-
cotics and cash deliveries in public parking lots, and fre-
quently use pagers and public telephones.” Id. at 909 n.4.

   [14] Similarly, in this case Shin offered extensive opinion
testimony regarding how he believed that Freeman’s words
and actions were consistent with the common practices of
drug traffickers. For example, Shin’s opinion on why Free-
man wanted to get off the phone, while an interpretation of a
seemingly innocuous statement, is not a violation of Rule
704(b). See id. at 908. Shin offered no opinion as to whether
Freeman possessed the requisite criminal intent to possess and
distribute cocaine, but instead described a common practice of
those who do have such intent. We conclude that no error
occurred. See United States v. Lipscomb, 14 F.3d 1236, 1239
(7th Cir. 1994) (citing cases in which courts have rejected
attempts to exclude drug expert testimony under Rule 704(b)
because the testimony “simply described in general terms the
common practices of those who clearly do possess the requi-
site intent, leaving unstated the inference that the defendant”
possessed such intent).
                   UNITED STATES v. FREEMAN                  7093
                III.   Freeman’s Other Claims

  A.   Broadening of Indictment

   [15] Freeman also argues that the district court impermiss-
ibly broadened the indictment at trial. The Fifth Amendment
guarantees a criminal defendant “[the] right to stand trial only
on charges made by a grand jury in its indictment.” United
States v. Adamson, 291 F.3d 606, 614 (9th Cir. 2002) (internal
citation omitted). “An amendment of the indictment occurs
when the charging terms of the indictment are altered, either
literally or in effect, by the prosecutor or a court after the
grand jury has last passed upon them.” Id. (quoting United
States v. Von Stoll, 726 F.2d 584, 586 (9th Cir. 1984)). A con-
structive amendment occurs where there is “a complex of
facts [presented at trial] distinctly different from those set
forth in the charging instrument,” or when “the crime charged
[in the indictment] was substantially altered at trial, so that it
was impossible to know whether the grand jury would have
indicted for the crime actually proved.” Von Stoll, 726 F.2d
at 586 (internal citation and quotation marks omitted). Free-
man argues that the evidence presented by the government
detailing Mitchell’s larger drug organization constituted an
amendment of the indictment.

   Freeman’s argument lacks merit. The government elicited
testimony from Shin about the investigation of Mitchell’s
drug trafficking because the testimony explained why there
were so many intercepted telephone calls. The limited evi-
dence offered by the government concerning the Mitchell
drug conspiracy gave context for the charges and outlined the
roles Mitchell, Brown, and Freeman had in the conspiracy.
The indictment alleged that Freeman had purchased cocaine
powder from Mitchell and Brown with the purpose of con-
verting the cocaine powder into cocaine base, which would
then be sold. Accordingly, the evidence offered by the gov-
ernment in connection with Freeman followed these alleged
drug transactions and focused on the recorded telephone calls.
7094               UNITED STATES v. FREEMAN
The evidence presented therefore complied with the indict-
ment, and Freeman’s Fifth Amendment rights were not vio-
lated.

  B.   Sufficiency of the Evidence

   Freeman contends there was insufficient evidence to sup-
port his conviction. We must affirm the conviction if, “view-
ing the evidence in the light most favorable to the
prosecution, any rational trier of fact could have found the
essential elements of the crime beyond a reasonable doubt.”
United States v. Shipsey, 363 F.3d 962, 971 n.8 (9th Cir.
2004) (quoting Jackson v. Virginia, 443 U.S. 307, 319
(1979)). To convict on a federal conspiracy charge, the gov-
ernment must prove “ ‘1) an agreement to accomplish an ille-
gal objective, 2) coupled with one or more acts in furtherance
of the illegal purpose, and 3) the requisite intent necessary to
commit the underlying substantive offense.’ ” United States v.
Chong, 419 F.3d 1076, 1079 (9th Cir. 2005) (quoting United
States v. Pemberton, 853 F.2d 730, 733 (9th Cir. 1988)).

   There were two main witnesses who testified for the prose-
cution, Shin and Mitchell. They testified regarding Freeman’s
involvement in various drug transactions including arrange-
ments made in numerous phone calls between Mitchell,
Brown, and Freeman. Freeman testified on his own behalf. He
contested Shin’s and Mitchell’s interpretations of those calls
and provided alternative meanings. The district court, during
the hearing on Freeman’s motion for a new trial, summarized
the opposing evidence:

    Well, the jury didn’t buy [Freeman’s testimony]. The
    jury, you know, believes it’s a credibility issue as to
    what Mr. Freeman testified that the conversations
    meant, [and] what the officer testified.

  [16] As the district court noted, this case came down to a
question of credibility. Freeman offers no argument challeng-
                   UNITED STATES v. FREEMAN                7095
ing the sufficiency of the evidence except to repeat his objec-
tion to the admissibility of testimony from Shin and Mitchell.
When reviewing the sufficiency of the evidence, however, we
“must assume that the evidence at trial was properly admit-
ted.” United States v. Vizcarra-Martinez, 66 F.3d 1006, 1009
(9th Cir. 1995). Aided by this assumption (which we have
examined and approved), we conclude that a rational trier of
fact could have convicted Freeman of conspiring to manufac-
ture and distribute cocaine base.

  C.   Allen Charge

   Freeman argues that the district court’s Allen instruction
had an impermissibly coercive effect upon the jury. In assess-
ing the coerciveness of an Allen charge, we consider “(1) the
form of the instruction, (2) the time the jury deliberated after
receiving the charge as compared to the total time of delibera-
tion, and (3) any other indicia of coerciveness.” United States
v. Daas, 198 F.3d 1167, 1179-80 (9th Cir. 1999).

   [17] Nothing in the instant case indicates coerciveness on
the part of the district court. The instruction given here has
been described as a “neutral form of the Allen charge.” United
States v. Steele, 298 F.3d 906, 911 (9th Cir. 2002) (discussing
9th Cir. Model Crim. Jury Instr. 7.7). The jury deliberated for
approximately three hours before announcing their deadlock
and for two hours following the Allen charge. This timing
does not give an indication of coercion. See Daas, 198 F.3d
at 1180 (approximately four hours of deliberations before the
Allen charge and one hour after did not indicate coerciveness).
No other indicia of coercion exist. We therefore conclude that
the district court committed no error in delivering an Allen
charge.

  D.   Sentence

  Freeman contests the reasonableness of his sentence. We
review the reasonableness of the ultimate sentence in light of
7096               UNITED STATES v. FREEMAN
the factors set forth in 18 U.S.C. § 3553(a). See United States
v. Booker, 543 U.S. 220, 260-62 (2005); United States v. Can-
trell, 433 F.3d 1269, 1279 (9th Cir. 2006). The district court’s
interpretation of the Sentencing Guidelines is reviewed de
novo, the district court’s application of the Sentencing Guide-
lines to the facts of a case for abuse of discretion, and the dis-
trict court’s factual findings for clear error. Id.

   [18] On this point, Freeman again refers to the testimony
offered by Shin and Mitchell, arguing that there was insuffi-
cient evidence that he was involved in the conversion of two
kilograms of cocaine. However, in a special verdict form the
jury found that Freeman’s crime involved between five hun-
dred grams and five kilograms of cocaine. The district found
that Freeman had converted at least two kilograms of cocaine,
and that finding is well supported by the record. The district
court did not abuse its discretion in calculating the guidelines
range. The district court sentenced Freeman to a term of
imprisonment fifty-two months below the bottom of the advi-
sory range. No basis exists for determining that the district
court’s sentence was unreasonable.

                       IV.    Conclusion

  We conclude that the issues discussed in this opinion do not
warrant reversal. Freeman’s conviction and sentence are
AFFIRMED.
