What's your pet rat laughing at?

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.

...just be careful not to trip or fall in front of your little buddy :o)