Continuity mistake: In the scene where Alex has just risen from the dead and escapes from the prison through the roof, there's a close up on him. His hair is much shorter in this shot then it was a few seconds ago. Then when he jumps down, his hair is longer again. This happens at least once more later in the film. (00:15:20)
Visible crew/equipment: Right before he discovers the knife that killed his girlfriend, someone's hand is visibly scaring the crow off the top of the filing cabinet. (00:18:00)
Continuity mistake: When Alex sees the cop hiding in the shower on the camera/web server towards the end, the hit counter is at the same level as it was earlier in the film (despite increasing steadily every second when we last saw it). Plus the mouse cursor is slowly moving up from "Camera 3" to "Camera 1", despite Alex not moving the mouse. (01:12:55)
Continuity mistake: When we see the police officer checking the hit counter on an adult web site, the hit counter goes down from 1,739,986 to 1,739,944 a few seconds later.
Revealing mistake: When Alex drops the cigarette lighter to ignite the gas, you can see the flame is started from a different source, as it starts on the other side of the screen, a fair distance away from where the lighter landed.
Revealing mistake: When Alex is about to peel off his burned skin to reveal his iconic "crow" face, you can tell where the makeup switches from attached prosthetics to the fake "pull away" makeup.
Revealing mistake: When Alex sees the arm in the burning rubble of the club, you can tell the arm is a prop because it is melting in spots, not burning up like real skin does.
