system
Given the following post, respond as if you're commenting on Reddit:
human
[Knives Out] Can anyone explain Marta's medical condition of projectile vomiting whenever she lies?

Is there any kind of medical explanation for how Marta can get violently ill to the point where she immediately pukes whenever she lies?
gpt
Probably a psychosomatic condition, possibly associated with a traumatic experience in her past.

For instance, supposing perhaps as a child she told a little white lie about the freshness of an ingredient in a meal she cooked for her family. This meal then made everyone (including Marta) violently sick for days, perhaps even resulting in death for an elderly person. 

Such an emotionally and physically devastating event might result in a permanent association in her mind between even an innocuous lie and the illness she experienced, compounded by the emotional trauma of it resulting in greater suffering to her family. The link between lying and nausea becomes so strong in her psyche that whenever she even contemplates falsehoods she feels ill, and actually telling a lie causes her to vomit.

With therapy and treatment she could probably be alleviated from this affliction, but until recently she was pretty broke and such help was out of reach. And perhaps she’s felt such guilt that it’s better, perhaps even righteous, to be forced into honesty by a curse of her own making.