Continuity mistake: When the film crew are making their movie in the tunnel, the short white guy is standing on some platform for a minute, and you can clearly see a member of the film crew in the background. Then they disappear.
Revealing mistake: Trevor Stark appears as the twin brother of Travis. They both have the same scar on their left cheek. Therefore they are the same person and not twins.
Audio problem: In the final scene, when the guy is shot by Reece Wilson, you hear her shoot 4 times. But you can see at least 5 wounds.
Visible crew/equipment: During the scene in the Professor's office, there is a pan of the campus through the window. The reflection of a crew member can be seen briefly in the glass, wearing a gold watch and moving something.
Continuity mistake: When Trevor is showing Amy the search he entered into the computer, Vanessa and Toby are both on the list. Why was Vanessa on it when she hadn't been attacked yet, and why was Toby on it when he hadn't been attacked at all?
Continuity mistake: Considering how carefully the killer cleaned the scene of Sandra's death, how likely is it that he would have left a cigarette at the scene of Simon's death? He didn't know that Amy was on her way out, so he wouldn't have rushed away from the scene.