1. The smell of the "fake" food. Molloy is locked in a windowless room and fed bland, processed food that he finds repulsive. The smell of it is described as "chemical" and "unnatural," causing him to gag.
2. The stress of his situation. He is being held captive and subjected to intense psychological pressure. The stress of his situation is described as overwhelming and contributes to his physical reaction, making him want to vomit.
The film uses these moments to highlight the psychological torture Molloy is subjected to and the lengths the government will go to to silence him.