Nightmares are familiar to humans, but it now seems rats can have them too. Gabrielle Girardeau and colleagues at New York University put rats in a maze and blasted them in the face with an unpleasant, yet harmless, burst of compressed air. As the rats slept later, patterns of activity arose in their hippocampi corresponding to their mental map of the maze, but activity in the amygdala, a region involved in emotion, also showed up whenever the blast of air was activated.