Other mistake: During the newscast after the girls are taken 3 photos are shown. Casey's photo looks to be a screen shot of her in the car whilst the abduction was taken place This is an impossible photo to have on the news.
Continuity mistake: When Casey locks the monster inside the room where he killed the girl, the lock on the door changes style when the monster opens the door. At first it's all flat and flush with itself, but the next time there's a cylindrical part raised from the base. (01:31:45 - 01:32:55)
Continuity mistake: Late in the film, after The Beast emerges, he partially devours two of the young girls like a ravenous animal; yet, when he catches up to the third girl, Casey, a few moments later, The Beast has no blood on his face, body or hands. Furthermore, when The Beast corners Casey in the cage, he presses his face between the bars, and we see no blood on his face. The camera cuts to Casey then back to The Beast, and now streams of blood are running from his mouth and down his chin. The camera cuts to Casey and back to The Beast once more, and now we see no blood on his face.Charles Austin Miller
Continuity mistake: Near the end of the movie when Casey is shooting at the Beast, she is wearing a white sweater, it's ripped a little, then in the next scene it's shredded to bits, hanging off her. When she locks herself in the cell the white sweater is almost completely gone.