The real-life Carla Moran's teenage son described a particularly vicious attack in which Carla was thrown by the malevolent force and hit her head. He tried to intervene, but he was also thrown, breaking his arm. In the filming of the movie, the actor playing the son broke his arm in that scene, and the curtains tore from top to bottom without explanation.
The method in which Carla is diagnosed by physicians, a method which relies heavily on her personal history, and in particular her relationship with her father and her sexual encounters with other men, reflects a largely Freudian psychodynamic method of diagnosis. This, combined with the fact that she is initially diagnosed by the team of doctors as having "hysteria," a disorder that has disappeared from mainstream American psychiatric diagnostics, makes this movie one of the last in which Freudian methods and conceptions (largely related to sex and childhood development) are shown to have a significant impact on the diagnosis of patients. With the rise of neurochemistry, neuroscience, and biological tests in the 1980s, 1990s and beyond, Freudian methods like those portrayed in the film would themselves become considered by many mainstream biological psychiatrists to be superstitious.
This movie was originally planned to be released in 1981 but did not debut in theaters until late 1982, with some territories including Australian and its American release in the U.S. not launching until early 1983. Generally, the film was released a short time after 1982's other poltergeist movie, Poltergeist (1982).
A whole dream sequence where Carla was forced to have incestuous thoughts about her son by the Entity was dropped for the movie by director Sidney J. Furie, because it was too sexually controversial at that time. This was despite the then recently released Bernardo Bertolucci film, Luna (1979), which examined a mother-son relationship and also being from the same 20th Century Fox studio.
This film was made and released about four years after its source novel of the same name by Frank De Felitta was first published in 1978. A frequent dust-jacket blurb for the book read, "Beyond physical reality, beyond ecstasy and pain, to a dark netherworld of psycho-sexual truth."
The trivia item below may give away important plot points.
The film's closing epilogue states, "The film you have just seen is a fictionalized account of a true incident which took place in Los Angeles, California, in October 1976. It is considered by psychic researchers to be one of the most extraordinary cases in the history of parapsychology. The real Carla Moran is today living in Texas with her children. The attacks, though decreased in both frequency and intensity...continue." According to an update by the Conneticut Paranormal Research Society web-page article titled "The Carla Moran Story, the Entity,""The woman [Carla Moran] moved five times, but the attacking entity followed her. She eventually moved further away. As she moved, the phenomena diminished, and after about two years, the attacks stopped altogether."