Vomit should smell bad

By dkl9, written 2024-148, revised 2024-148 (0 revisions)


Some months ago, after feeling sick for hours, after having refrained from it for years before, I vomited. The process was awful, vindicating my avoidance. Looking at the amount in the bucket, I figured "that has to be the entire contents of my stomach". Some minutes later, I vomited that amount again and then some.

The smell was the worst I remember ever encountering. In hindsight, it makes a lot of sense for vomit to have a particularly bad smell.

The main cause of vomiting, as an evolutionary adaptation, is food poisoning or gastric disease. Expelling something deemed harmful from the stomach prevents it being absorbed into the body. That some matter arose as vomit strongly suggests that the matter in question contains toxins or pathogens. This is perhaps the strongest reason to avoid eating vomit. Vomiting suggests the same, more weakly, of whatever was recently ingested, which implies that you should avoid eating food found near vomit.

The main effect of a "good" or "bad" smell is to provoke appetite or disgust, respectively. Disgust discourages one from eating and encourages them to get away from the bad smell. This is precisely the effective response after removing toxins via vomiting.

All of smell perception is subject to evolution, as are the compounds added to stomach-contents when vomited. Thus evolutionary pressure can almost arbitrarily reshape how we judge the smell of vomit. As the optimal response is disgust, the optimal smell is a bad one. The most reliably "bad" smell is an extremely bad smell. Hence the well-evolved vomiting animal would perceive an extremely bad smell just afterward.