William Peter Blatty is best known for his 1971 novel The Exorcist and for the Academy Award-winning screenplay of its film adaptation.

During World War I, almost every household in the U.S. had a Ouija board. In 1922, Ouija board sales even outsold Monopoly. But The Exorcist stopped the Ouija fad dead in its tracks. After watching the movie, many people destroyed their Ouija boards for fear of unintentionally inviting evil spirits into their homes.

After playing with a Ouija board and contacting a supposedly imaginary friend whom she calls Captain Howdy, Regan begins acting strangely, including making mysterious noises, stealing, constantly using obscene language, and exhibiting abnormal strength.

To sound as disturbing as possible, McCambridge insisted on swallowing raw eggs, chain smoking and drinking whiskey to make her voice harsh and her performance aggressive.

Chris hosts a party, during which Regan comes downstairs unannounced, tells one of the guests--an astronaut--that he will die in space and then urinates on the floor.

To create sound effects ranging from scratching in the house to the devilish noises, the sound effects crew recorded beagle dogs, pigs going to slaughter, and a trapped bee. In one instance, a variable speed oscillator was used to "tune" the buzzing of the bee to various pitches to create a chord cluster spanning four octaves.

Chris hears noises coming from the attic in the middle of the night and assumes she must have a rat infestation.

At the beginning of the film, Lankester Merrin, a veteran Catholic priest who performed an exorcism in the 1950s, is on an archaeological dig in the ancient city of Hatra in Iraq. There he finds an amulet that resembles a statue of Pazuzu, a demon of ancient origins with whom Merrin is familiar.

By the end of the film's production, nine people associated with its making had passed away, including Jack McGowran who played Burke Dennings, Linda Blair's grandfather, a night watchman on set, and a special effects expert.

In the scene where the words "help me" arise out of Regan's torso, the effect was achieved by constructing a foam latex replica of actress Linda Blair's belly, writing the words out with a paint brush and cleaning fluid, then filming the words as they formed from the chemical reaction.