system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does seeing other people vomit make us want to vomit?
gpt
The evolutionary advantage of "contagious vomit" is that in a group of people if someone got sick from something, it was likely others would to.  So...first person eats something poisonous or that has gone bad and makes you ill, then others wold get it out of their system _early_, rather than wait until genuine symptoms produced their own vomit.

It's _likely_ that this reaction was advantageous and increased likelihood of surviving as a trait - it would certainly prevent certain kinds of toxic materials from taking out an entire village if getting it out of your stomach early increased likelihood of survival.