popular conventional stories exploit the power of disgust. Villains from Harry Potter’s Lord Voldemort to Beowulf’s Grendel to The Texas Chainsaw Massacre’s Leatherface have disfigurements that fire these neural networks. In The Twits, Roald Dahl created a typically marvellous confabulation of the disgust principle: ‘If a person has ugly thoughts, it begins to show on the face. And when that person has ugly thoughts every day, every week, every year, the face gets uglier and uglier until it gets so ugly you can hardly bear to look at it.’
