Comment by garfieldnate

> It is even worse if the person smiles showing his/her teeth. In the animal world bare teeth are considered to be a threat. Hence I think there is some instinctive fear of bare teeth built into our social perception system.

I would love to hear from an evolutionary psychologist if this really is a thing in people. I remember being pretty astounded to learn that smiling monkeys are dangerous; there's no part of my consciousness that thinks of a toothy smile as dangerous.