Charles Darwin liked to freak out his friends—for science. He showed 24 guests in 1868 a set of “ghoulish” photos of a guy being prodded in the face with an electrical current. Darwin then asked his guests/guinea pigs to describe the emotion displayed in each photo. Darwin hoped to determine what universal core emotions exist (if any) and what culturally modified variations branch from them. The result was Darwin’s book The Expression of the Emotions in Man and Animals.