system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is smiling (showing teeth) considered friendly and reassuring in humans, but threatening in most other mammals?
gpt
When a human smiles, it's not the showing of the teeth that is the friendly part but the rest of the face around it. Baring of the teeth is relatively coincidental to the movements of the cheeks and look in the eye; a human can snarl threateningly just the same way any other animal would and that bares teeth just as much as a smile does. On top of that, we now know chimpanzees smile the same way humans do, just a bit less exaggerated.