Don't you laugh when you tickle yourself? Because I know I do. Only joking! The thing is that when someone tickles you, you don't laugh because you are being tickled; you laugh because you're surprised.

It's all to do with things going on in your brain. Part of your brain, called the cerebellum, is always looking for things happening to your body – such as being touched – so that it can make you react as quickly as possible.

Usually your body reacts only to things that your cerebellum thinks are important. When it expects something, such as you tickling yourself, the brain often doesn't think it's very important, so it tells your body not to do anything about it. But when something happens that your cerebellum isn't expecting, such as someone else tickling you, it doesn't have time to stop your body doing anything, and it makes you laugh.

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