I've found out why people laugh. They laugh because it hurts so much... because it's the only thing that'll make it stop hurting"
...
But that's not all people laugh at."
Isn't it? Perhaps I don't grok all its fullness yet. But find me something that really makes you laugh sweetheart... a joke, or anything else- but something that gave you a a real belly laugh, not a smile. Then we'll see if there isn't a wrongness wasn't there." He thought. "I grok when apes learn to laugh, they'll be people.

Autor: Robert A. Heinlein