A new study in the journal Bioacoustics found that 65 different species of animals have their own form of laughter. Study co-author Sasha Winkler describes the sounds animals make during play.

If you tickle a rat's belly, it squeals with laughter. However, we are unable to perceive this laughter as its frequency, around 50 kHz, exceeds the range of human hearing. Neuroscientist Jaak ...