Giggles, guffaws, or belly laughs -- whenever we crack up, we're communicating more than we realize. Laughter, says Dr. Sophie Scott, a neuroscientist at University College London as well as a standup comic, is pretty complicated. It's a way of expressing group membership and affection (as long as nobody is laughing AT you) and involves a physical reaction as well as an emotional one. Scott can make you laugh -- and then explain why you did!