In Knives Out, the new whodunnit from Rian Johnson, one suspect possesses what the loquacious detective Benoit Blanc (Daniel Craig) calls “a regurgitative reaction to mistruthing.” To put it in simpler terms: Whenever Marta (Ana de Armas) tells a lie, she pukes. (Those prone to sympathy gagging will perhaps be relieved to know the actress simply used baby food.) We won’t give away the answer to the movie’s big mystery, but for us this represented a smaller one: Is this a real medical condition or just a convenient plot device?
I called Dr. David A. Johnson, a professor of gastroenterology at Eastern Virginia Medical School and a past president of the American College of Gastroenterology, to ask if he’d ever encountered a patient with a similar “regurgitative reaction to mistruthing.” He hadn’t, but he did find it a plausible depiction of the brain-gut axis, the two-way communication link between the stomach and the brain that lets emotions mess with the digestive system’s equilibrium. “There are a lot of things that can upset that balance,” he said. “We do know too a lot of this is affected by gut bacteria, that the microbiome also is involved in this complex communication and regulation. There is a lot of science around this.”
With cases of chronic vomiting, he typically asks patients whether there’s a common trigger around episodes. “Never, at least in my 42 years of experience, has it been brought up that it was specifically around a lie, but emotional upset sometimes can be a trigger,” he said. “This is maybe what’s reflected in the lie, that the patient knows that it is disconcerting to their integrity.” As he would do when a patient has a food intolerance, Dr. Johnson would advise avoiding an emotional upset that is known to trigger vomiting. In other words: Don’t lie. “Politics is not an option for them,” he said.
Not lying isn’t always an option for Marta either though, and Dr. Johnson expressed concern for her health beyond these individual instances of lying and vomiting, noting that emotional stress can affect sleep and dietary intake. The brain-gut axis means that emotional turmoil can also affect bowel function in other ways, including cramping, constipation, and … diarrhea. That certainly would have made Knives Out a very different movie.