Continuity mistake: When Elliot's the basketball player, when he scores the slam-dunk and breaks the headboard, he breaks the headboard after the slam as he bounces/hangs off the headboard. But in the replay he breaks the headboard as he makes the slam and then bounces/hangs off the headboard. (00:49:10)
Continuity mistake: When the Devil is a teacher in the classroom she is erasing homework assignments off the board. In the close up shots (and maybe 1 or 2 of the far away ones) the board's partially erased. In most of the far away shots however, the board isn't erased. (01:01:50)
Factual error: When Elliot is the sensitive guy he picks up the guitar to sing a song to Allison. The guitar has a capo on it. During the song Elliot is changing cords and finger placement. He makes a cord above the capo. This would not be possible since the capo effectively cuts off the strings at the point of the capo. Any finger movement above the capo would not change the chord at all. (00:43:00)
Continuity mistake: At the very start of the film when Elliot is holding the door open for the people and they start to rush in at a very high speed, if you look closely about halfway through you will see the same people going in like in the first half of it (Especially look for a woman in a light blue suit). The clip is just being replayed.
Continuity mistake: Elliot is given a contract in the Devil's office. In one shot the contract is hanging off of the edge of the table. But a couple shots later, when the Devil picks up an apple and walks by the table, the contract is further onto the table, in a different position. (00:21:20)
Revealing mistake: During the opening sequence we see a lot of things happening very quickly and sped up. Everything is going in a progressive direction, not going backwards. As the sun rises in San Francisco a clock on a building is shown. The hands on the clock are going backwards instead of forwards. This was shot at dusk, not dawn, then reversed. (00:02:25)