Visible crew/equipment: As Chris walks around the attic a gas operated candle that doesn't have a wick is used in the shot when she's startled by the exploding flame. (00:30:45)
Visible crew/equipment: In his office as Chris talks to Doctor Klein the boom mike's reflection can be seen moving around in the metal light behind him. (00:34:45)
Visible crew/equipment: After Chris puts Regan to sleep she walks through an equipment shadow as she goes down the steps and asks the maid, "Is it coming out Willi?" (00:44:10)
Visible crew/equipment: After he stirs it, Det. Kinderman lifts the spoon out of his coffee as he starts to talk to Chris at the dinner table. A perfect reflection of the cameraman can be seen in the left of the spoon. (01:13:00)
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.
Visible crew/equipment: When the Fathers are exorcising Regan, as she floats above her bed, the boom is visible at the extreme top of the screen.
Answer: It was indeed Pazuzu, he wanted Regan to believe he was some friendly entity to gain her trust. Thus the Captain Howdy facade.