At the end when Dawn is tied by her hands, after she stabs Alex her hands are miraculously untied and the twist ties are missing from her wrist.
Dawn is wearing a necklace with a golden key on it the entire movie. About 1 hour and 23 minutes into the movie Dawn rips the necklace off her neck to open the box she found in Cori's bathroom. About 5 minutes later into the movie Dawn is walking out of the bedroom because the lights went out and she heard noises. In that scene the necklace can be seen around her neck again, which is practically impossible because a necklace chain ruptures when ripped off as Dawn did earlier.