RELIGIOUS groups have threatened to boycott cinemas in South Africa that are to start screening the horror movie The Exorcist on Friday. The powerful 1973 film by director William Friedkin tells the tale of how a demon takes possession of young girl, Regan, (Linda Blair) and her subsequent savage exorcism by a priest (Rod Steiger). Rhema church representative Ron Steel urged people not to watch the film as it dealt with ?something real, like the devil, and our view is that demonic powers can be stronger than Christians,? he said.