The mystery of ticklish laughter
As a behavioral and physiological phenomenon, tickling is a bag of riddles. Most young children instinctively giggle when tickled; yet prolonged tickling was one of the worst Medieval tortures. Aristotle raised the question of why one cannot tickle oneself. Surely, Christine Harris says, science should be able to explain tickling and the laughter it induces. And with some ingenious experiments, she is beginning to assemble answers. She finds, for instance, that when people believe they are being tickled by a machine, they laugh just as hard—suggesting that the laughter does not require an interpersonal context. In the article she explores the physiology of tickle (both annoying "light tickle" and laughter-inducing "heavy tickle") and its possible evolutionary function.