Plot hole: The book says the demon has to devour 5 souls in order for the abomination to return, but it only got 4 since David saved Mia's.
Suggested correction: In the extended version, we see Mia's soul isn't actually saved.
"In the extended version" has no relevance. Bonus content holds no weight when leveling criticism at the theatrical cut of a film.
Suggested correction: Actually, more than five souls were claimed over the course of the film, whether or not you count Mia. Four people died in the cabin, plus the possessed girl in the beginning of the film, in addition to the girl's mother, who is mentioned to have been killed by her. You could also make an argument that the dog counted, technically. You also gotta remember, the book said the souls must be "consumed," and technically, it did possess Mia and she "died" while still possessed before being revived. So by the vague definition of "consumed," she could still possibly count. Either way, definitely more than five souls were claimed over the course of the film.
Brother and friend were also technically cleansed by fire.
Continuity mistake: During the middle of the movie Mia rips off the buckwood necklace that her brother gave her at the beginning. She snaps and breaks it, but later in the film it is seen in one piece, and at the end she puts it on in an emotional expression of remembrance.
