This amazing study mapped the similarities of laughs across five species by tickling young gorillas, chimpanzees, bonobos and orangutans. They found that not only do they all laugh, but they share acoustic similarities with humans, especially babies (check out the audio samples). And just like humans, gorillas and bonobos laugh only when exhaling - just another example of how much we have in common with our closest cousins.
All of this reminds me of how sad I feel whenever I see an image of a chimp or an ape behind bars. It's not only because of the mental pain we are inflicting by isolating such a social creature (just like we are). But I think it's also because I feel that if we can't feel empathy for these animals, what hope do the rest have.