Poltergeists-the word is German for "racketing spirits"-were a mass of unknowns. Their physical disruptions of households served no discernible purpose of revenge, neither did they express the malevolence of a departed neighbor or kinsman, active even in death. Most poltergeists, in fact, could not be identified as spirits of the dead. If they did spring from the realm of death, they were anonymous envoys: They were bodiless and rarely visible, and their utterances almost never took shape as speech.

The details that recur in accounts of poltergeists hauntings only deepen the enigma. Poltergeists chose as targets the world's innocents: They had a predilection for the families of clergymen, and within those families they often singled out as the focus of their activities a young girl--a daughter or maidservant. Their---tactics---thumping, howling, the hurling of objects and creation of bad smells--seemed calculated to attract maximum attention with minimum physical harm.

That is not to say that a poltergeist infestation was a trifling inconvenience. Poltergeists had limitless stamina. Even gentle poltergeists mischief--slammed doors, upended cream pots, whiffs of sulfur--grew unendurable when the poltergeists sustained it day and night for weeks or months. And often much mild mischief was punctuated by bursts of destructive energy difficult to credit from an incorporeal and invisible spirit. Yet a few families, especially tolerant or humorous, grew inured to their spirit guests, after the inicial terror of the haunting faded. In time, a poltergeists might even come to be accepted as a slightly eccentric member of the family.