They bark, they play fetch, and they roll over. That's a given, after all - they're dogs.
But new research suggests dogs do something else when they're happy and playful: They laugh. (We're not joking!)
Patricia Simonet is one of the scientists who made this funny discovery. She works with animals at the Spokane (Wash.) County Regional Animal Protection Service.
In 2001, Ms. Simonet and a group of students at Sierra Nevada College in Lake Tahoe, Nev., had a theory about animal behavior. They thought dogs might have a sense of humor.
So the group recorded dogs at play and eventually isolated the whining, barking, and panting sound she now calls laughter.
You've probably heard doggy laughter. It's the long "huffing" noise they make when playing with a favorite toy or in anticipation of going on a walk.
Dogs even laugh when they're trying to encourage another dog - or person - to pay attention to them.
Animal play is nothing new, however. Scientists have long suspected that some animals smile or laugh.
Rats, for example, have been shown to chirp delightedly above the range of human hearing when wrestling with one another. Orangutans, chimpanzees, and gorillas also make laughing noises as they play.
So are these four-legged creatures the next stand-up comedians? Probably not, Simonet says. But be careful not to trip and fall the next time you're taking your dog for a walk. If your dog starts huffing, it might be at your expense!