What Is The Cause: People Being Ticklish?

I have also heard it was the bodies way of protecting itself. Think about where many people are ticklish: their sides, neck, and armpits. Those are all squishy places which don't offer much protection but have a lot to protect. I'm sure a few people are ticklish on their ribs but that might have more to do with the bone being so close to the skin so the nerves are kind of sensetive.