If they see shit splattered across the floor of a public toilet, or smell the decaying carcass of an animal lying dead in a ditch, or are touched by a visibly unclean stranger or a lecherous familiar, most people feel a physical reaction bordering on the emetic: they want to throw up. As you read this, perhaps you recoil at the very memory of these, with similar, negative sensory stimulations with feelings of ‘revulsion’, a word whose dominant meaning for the past two centuries is a ‘sudden, violent form of extreme disgust’ from which we are supposed to be hardwired to ‘back away.’