Not surprisingly, many horror movie villains suffer from serious mental illness, mental disorder, or physical ailments that can cause them to behave strangely. Become monsters who commit atrocities against innocent victims, stalking, murdering, raping, molesting and bullying their prey.
Sometimes a vicious cycle of torture, misery, insanity and criminality is created in which the victim becomes the victim of other victims who are often just in the wrong place at the wrong time. Their actions are so horrific that some people confuse their actions with demons, immortal goblins, mutants, ghosts, or demons themselves.
Although these films often allow supernatural and natural possibilities to explain the description of events, medical science usually allows for only one cause, although the cause, mental illness, applies to the villains and victims of films like Stephen King’s enormous, which take many forms to carry out, all horrifying and terrifying.
In writing The Exorcist, novelist and screenwriter William Peter Blatty took pains to ensure that Reagan MacNeil’s alleged demonic possession is assessed from the viewpoint of medical experts before the priests who come to her aid are permitted to perform the rite of exorcism. According to neurologist Suzanne O’Sullivan, M. D., the pre-teen’s condition could have been of a psychosomatic nature; Regan could have experienced “almost any symptom” due to her “distress—tremor, fatigue, speech impairments, numbness. Anything.”
On the other hand, Blatty also suggested that Regan’s condition might actually have been caused by demonic possession. Her fragile mental state might have opened the door, so to speak, to possession: “An entity cannot invade a living organism unless that organism or person’s personality is shattered,” he said. In his novel, the doctors’ best diagnosis is that the girl is suffering from “somnambuliform possession,” a condition in which “conflict or guilt . . . leads to the delusion that the patient’s body has been invaded by an alien intelligence or spirit”—in Regan’s case, a malevolent spirit that seeks her destruction. A doctor finally recommends that Regan’s mother Chris contact a priest.
The movie, which closely parallels the novel, also shows medical science’s attempts to explain Regan’s condition. After witnessing seemingly impossible physical actions on the girl’s part, Chris asks the doctor who examined her daughter how Regan could accomplish such feats. “Pathological states can induce abnormal strength,” the physician explains, as well as “accelerated motor performance.” He and his colleagues suspect that something is wrong with Regan’s “temporal lobe.” However, a battery of sophisticated tests uncovers nothing amiss.
Enter Father Lankester Merrin and Father Damien Karras. Although the former is more experienced in exorcism, he dies before the evil spirit can be cast out, and it is up to the younger priest to deliver the girl. At the cost of his own life, Father Karras succeeds, accepting the demon’s offer to leave Regan in order to take possession of him. Karras then jumps out of the girl’s bedroom window and falls to his death.
The movie hints at a conflict that the novel more explicitly indicates. Karras is a victim, too, of his own perceived neglect of his severely ill mother, who dies alone. Preying on Karras’s grief regarding his mother’s death, for which Karras blames himself, the demon tormented the priest during the exorcism. To escape his suffering might have been a secondary reason for the priest’s acceptance of the demon’s challenge that he trade places with Regan.