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We asked an expert if that stomach-turning condition in ‘Knives Out’ actually exists

A gastroenterologist explains whether a character’s extremely nervous GI track resembles any real ailments she’s ever encountered.

We asked an expert if that stomach-turning condition in ‘Knives Out’ actually exists
Ana de Armas (left) and Director Rian Johnson (right) on the set of Knives Out. [Photo: Claire Folger/Lionsgate]

People, by nature, are liars. Studies estimate that 60% of us can’t go 10 minutes without lying at least once, which probably explains why over half the people you meet at parties seem like they’re full of crap.

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Whether this vast league of liars is any good at lying, however, is another story. Most nonprofessional poker players have a tell or two when telling a fib, whether it’s gaze aversion, repetitive throat-clearing, or providing way too much bonus information unprompted.

The central character in Knives Out, however, just may have the absolute worst tell in the world.

Marta, the young caretaker played by Ana de Armas, has a condition in which any time she even considers lying, she has to throw up. Can’t control it at all. Once a detective (Daniel Craig) starts investigating the suspicious suicide of the wealthy author (Christopher Plummer) who employed Marta, the sleuth uses the caretaker’s condition to his advantage. Marta’s volatile GI tract is an internal human lie detector. It’s both a crucial plot device and the source of multiple sight gigs. But is it possible for someone to actually suffer from such a condition?

“I’ve never had a patient who got nauseous or throws up every time they lied,” says Dr. Kara Gross Margolis, a member of the American Gastroenterological Association. “But I think it’s a little bit of the stretching of a phenomenon that we see quite often, which is how significant anxiety can lead to nausea and vomiting.”

Dr. Margolis is a physician at Columbia University Medical Center, where she often deals with brain-gut disorders. Her initial focus was on autistic patients, and since individuals with autism tend to have a much higher rate of GI problems than the general population, she ended up searching for an explanation. In the years since, she has seen a full gamut of gastrointestinal patients with all sorts of psychiatric diagnoses—everything from anxiety and depression to ADHD and even bipolar and schizophrenia. Many of them have experienced heightened nausea in response to anxiety. But Dr. Margolis has never seen any patient quite like Marta. Because it’s quite possible that nobody has.

Ana de Armas (left) and Katherine Langford (right) in Knives Out. [Photo: Claire Folger/Lionsgate]
When I spoke to Knives Out‘s writer-director Rian Johnson recently for a separate piece, I asked whether the idea for Marta’s condition was inspired by any actual physical maladies he’d heard about.

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“That came completely from a story place,” Johnson told me. “The idea that someone we care about, they’re in an impossible situation, and their only tool to get out is by lying. Something I learned from [Breaking Bad creator] Vince Gilligan, you want to make life as hard as possible on the characters you love. So let’s take away her ability to lie.”

And take it away he does. Marta is unable to lie, and Johnson gets a lot of funny mileage out of her nauseated response to a number of different situations. According to Dr. Margolis, any one of these isolated incidents is entirely possible.

“When your body enters this extreme anxiety state and goes into sort of a fight-or-flight response, it results in a surge of hormones, and those hormones can absolutely cause gastrointestinal symptoms like the ones in the movie,” Dr. Margolis says. “So, you know, lying, I’ve never really heard of that or seen it in real life, but certainly under anxiety-provoking conditions, if someone was to be extremely anxious about lying, certainly they could get gastrointestinal side effects as a result of all of these things.”

(Left to right) Chris Evans, Ana de Armas, and writer-director Rian Johnson (right) on the set of Knives Out. [Photo: Claire Folger/Lionsgate]
Similar conditions to Marta’s exist, like Cyclical Vomiting Syndrome, where people get extremely anxious about some sort of social stress and it immediately results in episodes of nonstop vomiting. According to Dr. Margolis, the way to treat such anxiety-induced upchuck is to treat the anxiety. Perhaps Marta has experienced some unspecified trauma in her life related to telling a lie, and every time she attempts to do so now, the trauma is triggered anew. Marta’s condition only becomes farfetched with the idea that it has persisted this long (the character looks to be in her mid-twenties) without her ever seeking treatment.

Assuming that she has indeed never treated her anxiety, perhaps due to difficulties getting medical aid because of her immigrant status, is it medically possible that such a condition could continue sustained as long as Marta’s, if the underlying anxiety was just that overwhelmingly elevated?

“Certainly,” Dr. Margolis says. “There’s a lot of work done that the brain and the gut communicate to each other, and there are highways of communication that happen regularly.”

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After answering the big question at hand, I thank Dr. Margolis for her candor and apologize for asking some potentially uncomfortable questions. She laughs off the apology.

“It’s funny because nothing’s uncomfortable for me,” she says. “This is dinner conversation in my family.”

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