Vincent H. Gaddis

If you were to suddenly find objects flying around your room and crashing to the floor, hear unexplained knockings and thumpings, and see your lights turn on and off, you might think you have a poltergeist. Poltergeists, or "mischievous spirits," do all of these things and more. Most of their activities are merely annoying, but sometimes they can become dangerous.

People often think of poltergeists as a type of ghost. But researchers do not consider them to be ghosts. A ghost is typically defined as the spirit of a departed living being. A poltergeist, on the other hand, is directly connected to a living "focus person." That is, poltergeists' activities generally seem to be directed toward a particular person or somehow revolve around that person. The focus person is typically troubled, such as a teenager going through difficult puberty or a...