It is long known -- from Scripture, from centuries of Church experiences, from theology -- that purgatorial souls can on occasion send signs.

As Our Lady once said, "It happens that God permits them to manifest themselves in different ways, close to their relatives on earth, in order to remind men of the existence of purgatory and to solicit their prayers to come close to God, Who is just, but good."

What about "haunted" houses? Is there a connection with purgatory?

Adam Blai Adam C. Blai, a theological adviser (peritus) of religious demonology and exorcism in the Diocese of Pittsburgh, says (in an excellent new book, Hauntings, Possessions, Exorcisms), that we can follow certain standards in differentiating purgatorial souls from demons.

Notes the author:

-- Souls in purgatory are non-destructive in their signals.

-- Souls in purgatory do not make manifestations that are inherently terrifying; they usually limit them to a sound, a word, or a limited movement of objects.

-- Souls in purgatory limit their interaction with humans to signaling for help, and in rare cases the need for a particular wrong to be righted.

-- Souls in purgatory do not engage in prolonged communication or dialogue.

-- Souls in purgatory do not attack people physically.

-- Souls in purgatory do not attack religious or holy things.

-- Souls in purgatory become completely still and silent when prayer or Masses are offered for them.

Sometimes, writes the expert (who advises priests, and who was consulted in the famous "Brownsville haunting"), they may make the sounds of a person pacing or create odors that were associated with them; however, there is extremely limited speech, he says, "outside of a single phrase," such as "Help me." The most common such visitations come, he said, from those who have committed suicide or were homicide victims. "The other types of haunting that are common," says the author, who was trained in psychology, "occur in churches and religious housing such as rectories and monasteries."

Can demons drag along souls of the damned with them? Yes. Has Blai seen evil up close and personal? Before exorcisms, he was involved in prison work, where his clients included rapists, thieves, murderers, and serial killers. A graduate in clinical psychology from Penn State, he started out looking to see if alleged demonic possessions were "artifacts" and "pretty quickly found out there are things going on that are not explainable by science."

The urgent caution: demons "can take advantage of a known suicide or murder and pose as the victim," warns Blai. "Demons are attracted to places where people have attempted to communicate with spirits," he says, adding that "once demons gain the right to be extraordinarily active in a place, they often pretend to be human spirits seeking communication."

Their manifestations? These include black shadows, strange noises, the hearing of muddled or animal-like voices, bad odors, demonic nightmares, physical attacks (mysterious scratches or bruises), sleep deprivation, arguments and fights, and suicidal or homicidal ideation. They "hook" into our emotional wounds, negative thoughts, and sins.

And so it is that we interact on a constant basis with forces we don't normally see and against which we have a bubble of protection when we are pure inside and pray (and use Holy Water, especially before sleep).