 In the disturbing scene where Regan is masturbating with the  crucifix, a stunt double was used for the shot where Regan belts her  mother across the face. William Friedkin felt they needed someone  with more heft physically to perform the stunt, and the double was  shot from the back. The crucifix scene was filmed with Linda Blair,  who says she wasnt totally aware of what she was doing or the  implications of the vulgar acts.