Laughter is much older than language. Apes such as chimpanzees panting, laugh-like sounds when they and tickle each other. In humans, laughter is social. The researcher Robert Provine that people are about thirty times likely to laugh when they are with than when they are . Surprisingly, most laughter does not jokes at all, but ordinary such as ‘See you ‘.

Almost everyone has tried, and failed, to tickle themselves. The explanation lies in how the brain predicts the results of our own actions.

When we move, the brain sends a copy of the movement command to an area at the back of the brain called the cerebellum. Using this copy, the brain predicts how the movement will feel and reduces its response to the expected sensation. This is why our own touch feels weaker than someone else’s.

In a well-known experiment at University College London, Sarah-Jayne Blakemore and her colleagues used a robot to test this idea. Volunteers moved a lever that controlled a soft piece of foam touching their palm. When the foam moved at the same moment as their hand, it hardly felt ticklish. But when the researchers added a short delay of a fraction of a second, or changed the direction of the movement, the touch felt more ticklish.

This prediction system is valuable. By reducing our response to our own movements, the brain can pay more attention to unexpected events in the outside world, such as an insect landing on the skin.