Deliberate mistake: When Arthur is drawing letters of the alphabet, he only draws the outside of the letter A, not the horizontal stroke in the middle, yet it appears on the blackboard.
Deliberate mistake: Mitch carries Annie's body into her house through the front door, which he doesn't close behind him. In the next shot as he leaves the house it's been closed and he has to open it before he walks out. (01:32:20)