If you think laughter and comedy are reserved strictly for humans, you’d be wrong. A study in the late 1990s showed that creatures like rats emit ultrasonic vocalizations while playing with or anticipating the opportunity to play with other rats.

Tickling may seem like child's play, but scientists are beginning to see it as something much deeper—a complex puzzle tied to human touch, laughter, and brain development. The sensation of being tickled, known in scientific terms as gargalesis, is as old ...