“When a corrupting spirit is expelled from someone, it drifts along through the desert looking for an oasis, some unsuspecting soul it can bedevil. When it doesn’t find anyone, it says, ‘I’ll go back to my old haunt.’ On return, it finds the person swept and dusted, but vacant. It then runs out and rounds up seven other spirits dirtier than itself and they all move in, whooping it up. That person ends up far worse than if he’d never gotten cleaned up in the first place.”