Laughter:

"[A] key observation about laughter is that it's a vocalization, a sound. And across the animal kingdom, sounds serve the purpose of active communication. Cobras hiss to scare off predators. Dogs bark as a warning sign. Male birds sing to attract females, while baby birds chirp to let their parents know they're hungry. In all these cases, animals make noise because they want to be heard - because they want to affect their listeners in a predictable way. And so too does laughter."

Robin Hanson - The elephant in the brain