Visible crew/equipment: Near the beginning of the movie, the old priest is in Northern Iraq and you can see the shadow of a microphone on his hat.

The Exorcist (1973)
Ending / spoiler
Directed by: William Friedkin
Starring: Ellen Burstyn, Jason Miller, Lee J. Cobb, Linda Blair, Max von Sydow
Father Karras body is taken over by the demon that once possessed Reagan. In order to kill himself, Karras musters up the strength to leap out of the top story window to forever vanquish the demonic force residing in the house. Reagan is physically scarred, but flushed of the evil that once possessed her soul. (submitted by Vitascope)
Steve Lawton
Regan MacNeil: You're going to die up there.
Trivia: In the scene where Regan's mother is supernaturally blasted away from the bedside, she is being yanked by the crew by a length of rope. After dozens of takes director William Friedkin was still unhappy with the look of the shot and ordered the crew to haul her more fiercely. The scream in the shot that made the cut was of genuine pain and required no dubbing for effect.
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Answer: It was indeed Pazuzu, he wanted Regan to believe he was some friendly entity to gain her trust. Thus the Captain Howdy facade.