                     FOR PUBLICATION

    UNITED STATES COURT OF APPEALS
         FOR THE NINTH CIRCUIT


 UNITED STATES OF AMERICA ,                         No. 10-50253
                Plaintiff - Appellee,
                                                      D.C. No.
                      v.                           2:08-cr-00767-
                                                       PSG-2
 KENIA MUNGUIA ,
            Defendant - Appellant.
                                                      OPINION


         Appeal from the United States District Court
             for the Central District of California
         Philip S. Gutierrez, District Judge, Presiding

                    Argued and Submitted
             January 9, 2012–Pasadena, California

                    Filed November 27, 2012

Before: Stephen Reinhardt and William A. Fletcher, Circuit
      Judges, and Charles R. Breyer, District Judge.*

                   Opinion by Judge Fletcher;
                  Concurrence by Judge Breyer




 *
   The Honorable Charles R. Breyer, United States District Judge for the
Northern District of California, sitting by designation.
2                 UNITED STATES V . MUNGUIA

                           SUMMARY**


                           Criminal Law

    Reversing a drug conspiracy and possession conviction,
the panel held that the district court erred in refusing the
defendant’s requested jury instruction that the requisite
“reasonable cause to believe” that the drugs were being used
to manufacture methamphetamine must be evaluated from the
defendant’s perspective.

   Concurring, Judge Breyer wrote that defendants do not
have carte blanche to introduce scienter evidence of marginal
probative value that tends to “induc[e] decision on a purely
emotional basis” or run afoul of Fed. R. Evid. 403 factors.


                             COUNSEL

Karen Landau, Oakland, California for the Appellant.

Curtis Arthur Kin, Anthony James Lewis, Justin Randall
Rhoades, and Jennifer Leigh Williams, Office of the United
States Attorney, Los Angeles, California for the Appellee.

Sheryl Gordon McCloud, Seattle, Washington; Peter
Goldberger, Ardmore, Pennsylvania, Amicus Curiae,
California Partnership to End Violence, National
Clearinghouse for the Defense of Battered Women, and
National Association of Criminal Defense Lawyers.

  **
     This summary constitutes no part of the opinion of the court. It has
been prepared by court staff for the convenience of the reader.
                UNITED STATES V . MUNGUIA                    3

                         OPINION

W. FLETCHER, Circuit Judge:

    After a jury trial, Appellant Kenia Munguia was
convicted of conspiring to possess and of possessing
pseudoephedrine, knowing or having reasonable cause to
believe that it would be used to manufacture
methamphetamine, in violation of 21 U.S.C. § 841(c)(2). The
key question at trial was whether Munguia knew or had
reasonable cause to believe that the drugs she purchased were
being used to manufacture methamphetamine. Munguia
appeals her conviction. She contends that the district court
erred as a matter of law in refusing a requested jury
instruction specifying that “reasonable cause to believe” must
be evaluated from her perspective, based on her knowledge
and sophistication. The instruction given by the district court
provided that “reasonable cause to believe” should be
evaluated from the perspective of a hypothetical reasonable
person rather than from the perspective of Munguia. We hold
that the district court erred in refusing Munguia’s requested
instruction and that the error was not harmless.

                       I. Background

     Pseudoephedrine is a common ingredient in many over-
the-counter cold medications, including Sudafed, Claritin-D,
and similar cold-and-allergy medications. Pseudoephedrine
is a methamphetamine precursor. To combat the manufacture
and distribution of methamphetamine, federal law limits the
quantity of pseudoephedrine that retailers can sell to
individual consumers, as well as the quantity that individual
consumers can purchase.           Under the Combating
Methamphetamine Epidemic Act of 2005, retailers can sell
4              UNITED STATES V . MUNGUIA

only 3.6 grams of pseudoephedrine per day to any particular
individual. 21 U.S.C. § 830(d)(1). An individual can
purchase only nine grams in a thirty-day period. § 844(a). A
box of over-the-counter cold medication typically contains
2.4 grams of pseudoephedrine.

     To ensure compliance with federal and state law, many
retailers contract with MethCheck, a privately managed
database that tracks the purchase of drugs containing
pseudoephedrine. Retailers using MethCheck require that
purchasers of drugs containing pseudoephedrine provide
identification and an electronic signature at the time of
purchase. MethCheck records each purchase for which
identification is provided and keeps a record of the purchase
history of each purchaser.

    On June 13, 2008, the government charged Munguia,
Munguia’s boyfriend Edwin Alas, Alas’s brother David
Hernandez, and two others with illegally obtaining large
amounts of pseudoephedrine for use in the manufacture of
methamphetamine. Alas, the leader and organizer of the
group, quickly cooperated with the government and pled
guilty. An indictment was returned against Munguia and the
three others on July 1. It charged one count of conspiracy
“[t]o possess a listed chemical, namely pseudoephedrine,
knowing and having reasonable cause to believe that the
pseudoephedrine would be used to manufacture . . .
methamphetamine,” in violation of 21 U.S.C. § 841(c)(2).
(Emphasis added.) It charged a second count of “knowingly
and intentionally possess[ing] . . . approximately 184.8 grams
of pseudoephedrine, knowing, and having reasonable cause
to believe, . . . [that it] would be used to manufacture . . .
methamphetamine,” also in violation of § 841(c)(2).
(Emphasis added.) It was sufficient to convict under the
                UNITED STATES V . MUNGUIA                     5

indictment and under § 841(c)(2) that a defendant either knew
or had reasonable cause to believe.

    Munguia pled not guilty and went to trial. Munguia
admitted that she had purchased a significant amount of
pseudoephedrine at the direction of Alas. However, there
was starkly conflicting evidence about what Munguia knew
or had reasonable cause to believe about pseudoephedrine’s
role in the production of methamphetamine. Alas was the
government’s key witness on this question. He testified that
he told Munguia that the pseudoephedrine would be used to
make methamphetamine. Munguia testified that Alas had
told her no such thing. She testified that she had not known
that pseudoephedrine could be used to make
methamphetamine or that the purchase of cold medications
could be illegal. She attributed her ignorance in part to the
fact that, due to her fear of Alas, she had not asked him
probing questions.

    Munguia requested a jury instruction that would have told
the jury to decide whether Munguia “knew or had reasonable
cause to believe” based on what Munguia herself knew or
should have known, rather than on what a hypothetical
reasonable person had reasonable cause to believe. The
district court refused her requested instruction, instead giving
an instruction proposed by the government that referred
simply to “a reasonable person.”

    The jury convicted Munguia on both counts. We hold
that the district court erred when it refused Munguia’s
requested instruction and that the error was not harmless. We
do not reach other questions presented in this appeal.
6              UNITED STATES V . MUNGUIA

                  II. Standard of Review

     When a party properly objects to a jury instruction, we
review de novo whether the instructions given “accurately
describe the elements of the charged crime.” United States v.
Heredia, 483 F.3d 913, 921 (9th Cir. 2007) (en banc). We
apply harmless error analysis to determine whether an
improper instruction constitutes reversible error. United
States v. Thongsy, 577 F.3d 1036, 1040 (9th Cir. 2009).

                  III. Evidence at Trial

    At trial, the jury was presented with two irreconcilable
stories. Alas, the government’s cooperating witness, testified
unambiguously that Munguia knew that the pseudoephedrine
would be used to make methamphetamine. Munguia, who
took the stand on her own behalf, testified unambiguously
that she did not know. We summarize the conflicting
evidence in order to provide a basis upon which to evaluate
the disputed jury instruction.

             A. The Government’s Evidence

   MethCheck records introduced at trial established that
between February and June 2008, Munguia visited 564 retail
pharmacists and purchased 847 boxes of cold medication.
These boxes contained a total of 1,885.2 grams of
pseudoephedrine.

    Detective Tyrone Miles of the Los Angeles Police
Department testified that he observed Alas, Munguia, and the
other defendants as they spent a day going to pharmacies in
Los Angeles. Miles testified that Munguia drove the group
to eleven pharmacies on April 23, 2008. He stated that he
                UNITED STATES V . MUNGUIA                    7

followed the group into a store and “observed each one
approach the counter and purchase Pseudoephedrine
products.” Detective Miles testified that he saw the group
discard items in the trash as they left the pharmacies. Police
later retrieved these discarded items, which were identified as
empty cold medication boxes and receipts itemizing the
purchases. Miles testified that when he arrested Munguia,
she was seated near “a large amount of Pseudoephedrine pills
in a plastic bag.”         The car also contained “empty
Pseudoephedrine-based boxes, receipts, [and] cell phones.”
The pseudoephedrine pills were found rubber-banded in
packs of ten.

    Alas, Munguia’s former boyfriend and the government’s
star witness, agreed with the defense attorney on cross-
examination that he “very quickly made a decision to try to
work for the Government to get . . . out of some of the trouble
[he was] in.” Under his cooperation agreement, he pled
guilty and served only a month in jail before being released
pending sentencing. Testifying at Munguia’s trial was a
condition of Alas’s cooperation agreement. He admitted in
his testimony that he hoped his cooperation would result in a
reduced sentence.

    Alas told the jury that he began buying pseudoephedrine
pills in early 2008. He explained that he was recruited by “a
guy named Pirulin,” who asked him if he wanted to make
“easy money” purchasing cold medication. He claimed he
could not remember Pirulin’s real name. Alas testified that
he knew from the first day of his involvement with Pirulin
that the cold medication he purchased was used to make
methamphetamine. He testified that the first time he
purchased the medication, “store clerk[s] started asking [him]
questions. They would say, ‘Are you making meth with these
8               UNITED STATES V . MUNGUIA

pills? What are you doing? Why are you buying them?’”
Alas testified that when he asked Pirulin, he was told that the
drugs were being used to manufacture methamphetamine and
was warned to be careful.

      Alas testified that he brought Munguia into the project
several weeks later, when Pirulin asked him to begin
recruiting people to assist him. He testified that he thought
Munguia would be “a good candidate.” He testified that she
had been complaining that he was not spending enough time
with her, and that “she was out of a job and . . . wanted to
make money.” According to Alas, Munguia agreed to
participate immediately. He told the jury that she “offered
. . . to bring her auntie into this business because she worked
at a pharmacy and she could get more Sudafed pills . . . .”
Alas testified that Munguia told him that she would “get right
to it, and that day she went out to stores by herself, and by the
next day she had a couple boxes.”

    Alas testified that when he first recruited Munguia, he did
not explain why the pills were valuable. However, he said
that she came to him the day after she purchased her first
boxes of cold medication and asked “why were the clerks
asking her those questions.” “She specifically said those
questions, are they being used to make meth, and I told her
yes.” Alas testified that he warned her that “if she’s going to
start doing this . . . to be careful, make sure nobody is
following you because she could get in trouble for it.” Alas
further testified that he heard the clerks ask Munguia, “‘Are
you making meth with these pills?’”

    On cross-examination, Alas admitted that in August 2008,
after he had agreed to cooperate with the government and
after Munguia and the others had been indicted, he had told
                UNITED STATES V . MUNGUIA                      9

government attorneys and agents that he did not remember
telling Munguia that the pills were used to make
methamphetamine. Alas first explained his memory failure
by stating that their questions did not focus on Munguia. He
testified, “[T]he only reason I didn’t tell them . . . [was]
because we were focusing on other people and who I was
selling to, and Kenia Munguia wasn’t the primary focus in
that meeting.” He said that his current testimony did not
contradict his previous statement to the government: “If you
read carefully, it says that I do not recall, I do not remember.”
On further cross-examination, Alas changed his story. He
admitted that the government attorneys and agents had
specifically asked him whether he had told Munguia that the
pills were used to make methamphetamine. He admitted that
he had answered, in response to their specific questioning,
that he did not remember telling Munguia that the pills were
to be used for that purpose.

    Alas testified that Munguia usually drove him to locations
where he would sell the cold medications for $25 to $27 per
box. He testified that Munguia would remain in the car or
stay outside when he went to sell the pills. He testified that
upon returning to the car, he immediately shared the proceeds
with Munguia, giving her the entire amount he received for
each box that Munguia had purchased. He testified that he
treated Munguia as his equal partner and that he never made
a profit off the pseudoephedrine she had purchased.
“[W]hatever she purchased, whatever . . . she gave me, what
she bought out of her pocket, that’s what she got . . . . I
wasn’t taking no money out of what she purchased.” Alas
testified that sometimes he and Munguia each made $1,000
in a day.
10              UNITED STATES V . MUNGUIA

    On direct examination, Alas testified that he once slapped
Munguia after an argument at a nightclub. He said, “[W]e
were talking and she got very argumentative, and that’s when
I slapped her.” On cross-examination, Alas denied hitting
Munguia on any other occasion.

                  B. Munguia’s Evidence

     Munguia’s sister Jennifer testified that she had seen Alas
hit Munguia. She said she had been with Alas and Munguia
at a nightclub in late May 2008. Jennifer said that they
argued when Alas refused to give Munguia the keys to her
car. A security guard intervened at Munguia’s request. He
required Alas to return the keys and then evicted him from
the club. Jennifer testified that Alas came to their house later
that evening. “He started yelling at my sister and he grabbed
her by the arm. And he hit her like this, like with a closed
fist. And he hit her and he started screaming at her. And my
sister asked us to please call 911. And my cousin did it . . . .
So Edwin came and he grabbed my sister and he took her out
of the house.” Jennifer testified that after Alas learned that
911 had been called, “he told me that if I did it, that I was
going to pay the consequences for getting involved.”

    Munguia testified on her own behalf. She came to the
United States from El Salvador when she was about thirteen.
She left school in the United States after completing the ninth
grade. Because her English skills are limited, she testified
through a translator. Munguia admitted that she had
purchased a large amount of pseudoephedrine over a period
of several months. She testified, however, that she did not
know that the cold medications she purchased would be used
to manufacture methamphetamine.
                UNITED STATES V . MUNGUIA                   11

    Munguia testified that she met Alas in May 2007, and that
they began dating in July of that year. At the beginning, “[h]e
was a nice person to me,” but in August 2007 they had an
argument and Alas “turned very violent.” She testified that
Alas “is a very violent person.” She testified, “He used to
insult me verbally and he even slapped me . . . . He would
pull my hair.” She explained, “He wasn’t violent all of the
time with me. After he would abuse me, he always asked for
forgiveness. And I wanted things to be fine between him and
me. I felt lonely and depressed. And I tried my best so that
he would be happy with me.” She testified that it was
common for Alas to slap her if he thought she was being
argumentative. She testified that he had punched her in the
face with a closed fist, but that “he always tried not to leave
marks.”

    Munguia testified that Alas first asked her to purchase
cold medication in February 2008. She testified that he took
her to a store and bought pills, so that he could show her how
to buy them and what kind to purchase. That same day, she
explained, he took her to at least one more store, where she
purchased the pills herself. On cross examination, she
testified that she was unsure whether Alas had in fact
purchased pills that first day. She testified that she bought
pills from February through June 2008 “[b]ecause he was
asking me to.”

    Munguia testified that she earned nothing from her
efforts. She testified that at the beginning Alas gave her $100
or $200 “[e]very day in the morning” to buy pills. She said
that they then had an argument because Alas believed that she
was “keeping his change.” Thereafter, Alas would give the
exact amount at the store or would give her only $20.
12             UNITED STATES V . MUNGUIA

   Munguia directly contradicted Alas’s testimony that he
gave her the profit from each of the boxes of pills that she
purchased:

       Q: [Y]ou heard him testify how he would go
       sell the pills and then give you the money, 25,
       $27 or so per box for every box you had
       purchased. You heard that testimony, right?
       A: I did hear that.
       Q: Is that true?
       A: No.
       Q: Were you a partner with [Alas] in this?
       A: No.
       Q: Apart from maybe having kept the change
       at the end of a day early on, did you make any
       money at all from this?
       A: No.
       Q: And how were you getting by during this
       time if you weren’t making money from
       [Alas]?
       A: I asked my mother for money.

    Munguia testified that during the time she was purchasing
pills she “didn’t even have any idea what methamphetamine
was.” She testified that she twice asked Alas why they were
purchasing the pills. “The first time he told me that it was
better for me not to know.” She testified that she did not ask
Alas any further questions at that time:

       Q: Did you ask him any more questions after
       he said that?
       A: No, because he answered that in not a very
       nice way.
                UNITED STATES V . MUNGUIA                   13

       Q: And so why didn’t you ask him a follow-
       up question?
       A: I was always afraid of asking him
       anything.
       Q: And why is that?
       A: Because he was a violent person and he
       always answered me in a nasty way, and I
       didn’t like him to yell at me.

She testified that the second time she asked, he answered that
“he and his friends would take them with Red Bull.” She said
that she was not satisfied with his answer but did not inquire
further. She testified that he offered to give her some to try,
but that she refused.

    Munguia told the jury that when she bought the pills she
was asked for identification by store clerks and was required
to sign her name. She said that she took this as evidence that
her purchases were legal:

       Q: Did that concern you at all that you were
       buying these pills using your correct
       identification and so forth?
       A: No. I thought it was legal. It was legal to
       me because I was showing my I.D.

                 IV. The Jury Instruction

     Munguia was charged with conspiracy “[t]o possess a
listed chemical, namely, pseudoephedrine, knowing and
having reasonable cause to believe that the pseudoephedrine
would be used to manufacture . . . methamphetamine” in
violation of 21 U.S.C. § 841(c)(2) and with “knowingly and
intentionally possess[ing] . . . approximately 184.8 grams of
14              UNITED STATES V . MUNGUIA

pseudoephedrine, knowing, and having reasonable cause to
believe, . . . [that it] would be used to manufacture . . .
methamphetamine” in violation of § 841(c)(2). Munguia
objected to the government’s proposed jury instruction that
explained the “reasonable cause to believe” standard.

    The government requested the following jury instruction:
“‘Reasonable cause to believe’ means that the defendant
subjectively knew facts that either caused her or would cause
a reasonable person to believe that the pseudoephedrine
would be used to make illegal drugs.” (Emphasis added.)
Munguia objected to this instruction. Her proposed
instruction read: “‘Reasonable cause to believe’ means that
the defendant subjectively knew facts that either caused her,
or would have caused a reasonable person in her same
position, to believe that the pseudoephedrine tablets would be
used to make illegal drugs.” (Emphasis added.) The court
gave the government’s proposed instruction.

    Our cases make clear that the district court erred in
rejecting Munguia’s proposed instruction. In United States
v. Kaur, 382 F.3d 1155, 1156 (9th Cir. 2004), defendant Kaur
was a retailer who sold large quantities of cold medications.
Kaur was charged with violating 28 U.S.C. § 841(c)(2). Id.
She had requested an instruction that effectively would have
required the jury to find that she had actual knowledge that
the pseudoephedrine in the medication would be used to
manufacture methamphetamine. Id. at 1157. We upheld an
instruction that allowed the jury to convict based on a finding
that Kaur had reasonable cause to believe that it would be so
used. Id. at 1156. We agreed with the Tenth Circuit in
United States v. Saffo, 227 F.3d 1260 (10th Cir. 2000), which
had interpreted § 841(d)(2), now § 841(c)(2), to require an
                UNITED STATES V . MUNGUIA                    15

evaluation of the subjective state of the mind of the particular
defendant. We quoted Saffo:

           “[T]he standard involves a subjective
       inquiry that looks to whether the particular
       defendant accused of the crime knew or had
       reasonable cause to believe the listed
       chemical would be used to manufacture a
       controlled substance. This requires scienter
       to be evaluated through the lens of this
       particular defendant, rather than from the
       perspective of a hypothetical reasonable
       man.”

Kaur, 382 F.3d at 1157 (quoting Saffo, 227 F.3d at 1268-69)
(emphasis added). We wrote, “The district court explained
that [its instruction] incorporates both subjective and
objective elements: Ms. Kaur had reasonable cause to believe
if she actually knew facts that would alert a reasonable person
that the pseudoephedrine would be used to make
methamphetamine.” Id. at 1157.

    In United States v. Johal, 428 F.3d 823, 825-26 (9th Cir.
2005), defendant Johal, like Kaur, was a retailer who sold
large quantities of cold medications. Johal was prosecuted
under § 841(c)(2), and we upheld a jury instruction that
allowed conviction under the “reasonable cause to believe”
standard. Id. at 825. Relying on Kaur, we wrote,
“[R]easonable cause to believe is not purely objective, but
turns on the facts actually known by the defendant in a
particular case—facts from which the jury can infer that any
reasonable person in the defendant’s position would have had
to know that the ingredients were being bought to make
16             UNITED STATES V . MUNGUIA

illegal drugs.” Id. at 828 (emphasis in original). As we did
in Kaur, we quoted the Tenth Circuit’s decision in Saffo:

       As a practical matter, . . . the differences
       between actual and constructive “knowledge”
       under the statute are not substantial. See
       United States v. Saffo, 227 F.3d 1360, 1268-
       69 (10th Cir. 2000) (holding that the
       “reasonable cause to believe” standard in
       § 841(c)(2) “requires scienter to be evaluated
       through the lens of this particular defendant,
       rather than from the [perspective] of a
       hypothetical reasonable man” and likening the
       standard to actual knowledge).

Johal, 428 F.3d at 828 (emphasis added).

    Our opinions in Kaur and Johal make clear that the
“reasonable cause to believe” standard of § 841(c)(2) requires
a jury to evaluate scienter through the lens of the particular
defendant on trial. Under § 841(c)(2), a jury must decide
what the particular defendant on trial knew, and what that
particular defendant had “reasonable cause to believe.” The
scienter requirement of § 841(c)(2) is not satisfied if some
hypothetical person would have had “reasonable cause to
believe” that cold pills would be used to make
methamphetamine. The jury must therefore be instructed to
consider the knowledge and sophistication of the particular
defendant on trial, not that of a hypothetical reasonable
person not before the court.

    The government’s instruction merely asked the jury to
decide whether “a reasonable person” would have had cause
to believe that the cold pills would be used to manufacture
                UNITED STATES V . MUNGUIA                    17

methamphetamine. The district court erred in giving this
instruction because it did not direct the jury to evaluate
scienter “through the lens of the defendant,” as required by
§ 841(c)(2).

                    V. Harmless Error

    An error in describing an element of the offense in a jury
instruction is harmless only if it is “clear beyond a reasonable
doubt that a rational jury would have found the defendant
guilty absent the error.” Neder v. United States, 527 U.S. 1,
18 (1999). See also Thongsy, 577 F.3d at 1043. We conclude
under this standard that the erroneous jury instruction was not
harmless.

     Munguia’s sole defense was that when she purchased
large quantities of cold medication containing
pseudoephedrine she did not know or have reasonable cause
to believe that the medication would be used to manufacture
methamphetamine. If the jury believed Alas’s testimony, the
jury could have convicted Munguia under § 841(c)(2),
concluding that she knew or had reasonable cause to believe
that the medication would be used to manufacture
methamphetamine. However, if the jury believed Munguia,
it could have acquitted her. It could have concluded that the
nature of her relationship with Alas was such that her fear of
him prevented her from asking probing questions. It could
have concluded, in light of her lack of knowledge and general
lack of sophistication, that she did not know that the
medication would be used to manufacture methamphetamine,
and that, viewing the evidence through her “lens,” she did not
have reasonable cause to believe that it would be so used.
18               UNITED STATES V . MUNGUIA

    In its closing argument, the government characterized the
reasonable cause to believe standard as “the real sticking
point of the case.” It argued that “even if [the jury] believe[d]
the defendant, . . . the evidence, as applied to the law, . . . still
leads to a guilty verdict because the defendant is guilty if she
knew or if she had a reason to believe.” It explained the
“reasonable cause to believe” standard to the jury:
“Reasonable cause to believe means that the defendant knew
facts that either caused her to actually know or would cause
a reasonable person to believe that the Pseudoephedrine . . .
was being used to make an illegal drug.” (Emphasis added.)
The government argued that Munguia was “guilty even under
her story” because “a reasonable person would have known
that these pills were being used to make methamphetamine.”
(Emphasis added.)

    The government stressed that the jury could convict
Munguia based on what a hypothetical reasonable person
would have had cause to believe. The government argued
that “it all boils down to did the defendant know, should the
defendant have known, would a reasonable person have
known.” (Emphasis added.) The government continued,
“And the defendant’s actions, the defendant’s own choices,
overwhelmingly answer that question again and again. Yes,
the defendant knew. Yes, the defendant should have known.
And yes, a reasonable person would have known.” (Emphasis
added.) “This defendant, in less than three months, walked
into CVS pharmacies over 550 times, and she bought over
800 boxes of Pseudoephedrine pills. Those pills were being
used to make methamphetamine. The defendant knew that.
And a reasonable person would have known that.”
(Emphasis added.)
               UNITED STATES V . MUNGUIA                   19

   Munguia’s attorney tried to convince the jurors that they
should evaluate the “reasonable cause to believe” standard
from the perspective of “a reasonable person in her position.”
He asked:

       So who is this reasonable person? Is it
       Special Agent Bradley Clemmer who testified
       as to how methamphetamine is made from
       Pseudoephedrine? He seems like a reasonable
       enough person. Is it Jennifer Williams [the
       prosecutor]? She seems like a reasonable
       enough person. Is it me? I think I’m a
       reasonable person.

He then answered his own question:

       No it’s not. And why not? It’s a reasonable
       person in the position of the defendant.
       Someone young, recent immigrant,
       little–some formal education, through the
       ninth grade with some difficulty–and in the
       position she was in with Mr. Alas with
       all–with everything that went on that. With
       all of the choking down of being able to ask
       any questions and all of that. So that is the
       standard that is to be applied here. It’s a
       reasonable person in her position.

He argued that “this young, unsophisticated woman with little
formal education was naive. No reasonable person in her
position would have known.”

    However, the district court instructed the jurors to apply
the government’s rather than Munguia’s theory of scienter.
20              UNITED STATES V . MUNGUIA

The court directed jurors to look to the instructions, and
nothing else, in determining the applicable law. The first jury
instruction specified that jurors were to “apply the law as I
[the district court] give it.” The court emphasized that jurors
“must follow the law as I give it whether [they] agree with it
or not.” The court cautioned that the “verdict must be solely
based on the evidence and on the law as I have given it . . . in
these instructions.”

    Because the instruction specified that Munguia’s
“reasonable cause to believe” defense should be evaluated
based on what a hypothetical reasonable person would have
had reasonable cause to believe, the jury was compelled to
look to the scienter of that hypothetical reasonable person.
Based on its understanding of the “reasonable cause to
believe” standard, the government argued to the jury that
even if it believed all of Munguia’s testimony, it was still
required to convict. But the jury instruction and the
government’s understanding were incorrect. If it had
believed Munguia’s testimony, and if it had been instructed
to view Munguia’s mens rea through her “lens,” the jury
could well have acquitted her. We do not find it “clear
beyond a reasonable doubt that a rational jury would have
found the defendant guilty absent the error.” Neder, 527 U.S.
at 18. We therefore conclude that the erroneous instruction
was not harmless and that Munguia’s conviction should be
reversed.

                      VI. Other Issues

   Munguia and an amicus argue strenuously that the district
court improperly excluded expert testimony of a psychologist
who would have testified that Munguia suffered from battered
woman syndrome, and that this syndrome was relevant to
                UNITED STATES V . MUNGUIA                      21

whether Munguia knew or had reasonable cause to believe
the cold medication would be used to manufacture
methamphetamine. It is unclear whether the district court
would have excluded the proffered testimony if it had
understood that “the reasonable cause to believe” standard
under § 841(c)(2) must be evaluated with respect to the
particular defendant before the court rather than with respect
to a hypothetical reasonable person. It is also unclear what
expert testimony might be proffered at a second trial, should
there be one. Under these circumstances, it is neither
necessary nor appropriate for us to opine on the correctness
of the district court’s exclusion of the proffered testimony.

  It is also unnecessary to address other issues raised by
Munguia.

                          Conclusion

    We hold that the district court erred in failing to give
Munguia’s requested jury instruction and that this error was
not harmless. We therefore reverse Munguia’s conviction.

    REVERSED.



BREYER, District Judge, concurring:

      District courts serve as gatekeepers responsible for
admitting relevant evidence, except where the probative value
of that evidence “is substantially outweighed by a danger of
. . . unfair prejudice, confusing the issues, misleading the jury,
wasting time, or needlessly presenting cumulative evidence.”
Fed. R. Evid. 403. While the Court today has correctly stated
22             UNITED STATES V . MUNGUIA

the standard for what it means to have a “reasonable cause to
believe” under § 841(c)(2), the gatekeeper function remains
unchanged. Accordingly, defendants do not have carte
blanche to introduce scienter evidence of marginal probative
value that tends to “induc[e] decision on a purely emotional
basis” or run afoul of the familiar Rule 403 factors. See Fed.
R. Evid. 403 & advisory committee’s note.
