Material: Mob psychology, multiple sclerosis, chimp communication and shrunken heads.

This week Quentin Cooper investigates the psychology that turns a peaceful protest into a rioting mob. He hears about a major international study that is tracking down the genetic background to multiple sclerosis. As a new documentary is released about Project Nim, he revisits the classic experiment to bring a chimpanzee up like a human child. And he learns how Amazon tribes shrank human heads.