TonyPH

Father Lamont: It was horrible. Utterly horrible. And fascinating.

TonyPH

Stupidity: Dr. Tuskin says Regan's exorcism has made her psychological problems worse. Not only would Dr. Tuskin have to be grossly misinformed about Regan's condition prior to the exorcism to hold such an opinion, Regan's current "problems" appear to consist entirely of nightmares and absent parents, and she is otherwise shown to be a healthy, well-adjusted teenager.

TonyPH

Plot hole: Dr. Tuskin warns that if Regan were to remember the events of her possession it could be so traumatic for her it could lead to suicide, even though Regan's therapy seems to be based almost entirely on what she can remember about the events of her possession.

TonyPH

Factual error: Father Lamont tears out the Regan doppelganger's heart from where her stomach should be. Even allowing that she's a manifestation of a demon and may not conform to human anatomy, it isn't plausible that Lamont would know to grab for her heart through her abdomen.

TonyPH

Stupidity: I won't begrudge Father Lamont for instinctively grabbing for the first thing in reach to try to smother the box on fire (even if it is a pair of wooden crutches), but you'd think at some point he'd notice that he's just spreading the fire and making it much, much worse, but he keeps at it until the doctor finally returns with the extinguisher.

TonyPH