Why is showing teeth a sign of aggression in animals but not in humans?

Well rude kids sometimes show you their teeth like in an agresive way...

And some people, uneducated people would do to and even bite.

Humans do it too in a smaller degree, lift upper lip to reveal teeth when thoroughly pissed

Errrrrrrrr!!!!! Gimme me dat banjo! Grrrr

Because we don't eat fellow humans or fight them that way.

cause some animals do that to show aggression and some don't, including humans

Uhhh when a woman smiles and she's not happy it's scary stuff.

It actually can be a microexpression in humans.

Because animals usually bite.

[image deleted] it can be