When something is ticklish, it means it makes you laugh or squirm when touched lightly. Most people are ticklish on their feet, ribs, or neck. Even the gentlest touch in these spots can cause an uncontrollable giggling fit. Scientists aren't entirely sure why we're ticklish, but it seems to be the body's way of protecting sensitive areas. Your nervous system goes on high alert when something brushes against vulnerable spots, and laughing might be an ancient reflex that makes potential threats back off.

Interestingly, you can't tickle yourself. Try it right now: run your fingers along the bottom of your own foot. Nothing happens. Your brain knows what to expect when you touch yourself, so it doesn't trigger the ticklish response. But when someone else does it, your brain can't predict exactly when and where the touch will come, so you react.

The word also describes situations that require careful handling. A ticklish situation is one that's delicate or risky, like when a teacher asks why two friends are arguing and you have to explain without making either friend angry. A ticklish problem needs to be handled gently and thoughtfully, much like you'd approach someone who's, well, ticklish.