For this week's 'Weird Science' segment on Breakfasters, Dr Jen explains the science behind tickling. Did you know there's two different kinds of tickling? There's knismesis, the kind that feels like something light and feathery has brushed past your skin, but doesn't make you laugh, and there's also gargalesis, the kind that feels unpredictable, and that makes you laugh and squirm! Why do we laugh though, if it's so uncomfortable? Are there biological and evolutionary reasons for this?