Invisible cats are the bane of light sleepers. Though they cannot be seen, they can be both felt and heard. They delight in leaping from heights onto bedspreads, scratching at doors, and knocking small objects from shelves. Should a nearby human wake, the invisible cat will freeze, remaining absolutely silent until they start to sleep again — at which point the harassment resumes. Invisible cats live in family groups of up ten, who take it in turns to torment individual insomniacs. If you think you may be suffering an infestation, you are advised to throw catnip through your open windows. With luck the cats will follow, and you can then close the windows to keep them out. Of course, since they are invisible, you won't be able to tell if it worked.