Continuity mistake: When Mitch is closing the shutter after the birds have started to fly into the window you can visibly see blood on the shutter, yet when they switch cameras and he shuts the shutter the blood is gone. (01:42:05)
Deliberate mistake: When Melanie first walks into the classroom she sees five rows of students. Later when the students are about to leave there are only four rows of students, now ending with the boy in the plaid shirt (closest to the camera), in the front. The row on the left has been removed so the camera can pan from left to right in the side shot. (01:08:50 - 01:13:00)????