[Duchess]

The Exorcist

Friedkin William, the director of The Exorcist, went to great lengths to keep his cast off balance and on edge so that the intensity would translate onto the screen. He was known to have crew members sneak up behind actors and fire air guns to scare them. When Linda Blair and Ellyn Burstyn had to film scenes involving harnesses, he demanded that they both be shaken more violently and longer than necessary; they were both injured in the process. Father Dyer, who was played by a real priest rather than an actor, was smacked in the face by the director right before a scene.
Father O'Malley, the priest who played Father Dyer, was involved in the case that inspired the movie. He claims that the plot of the movie is based on an exorcism of a young boy in Maryland and that the movie is 80 percent factual.