Continuity mistake: When Romey hits the little boy, she immediately parks her car and gets out. She closes the door behind her and runs to the little boy. After making sure he is ok, she goes back to her car and the door is open.
Continuity mistake: At the beginning of the scene in which Romy hits the little boy with her car, the camera is following behind her car. We see that she is about to pass a parked SUV on the left side. The camera then cuts to inside the car looking at Romy and the driver side window, and we never see the SUV that she was just about to pass. (00:49:15)
Factual error: The Book of Mirrors is a rare medieval manuscript, yet Casey has no problem whatsoever in bringing the book to Rabbi Sendak. No library would lease such a valuable item and stealing it would also be rather difficult, as you are supposed to deposit a document and fill out a request form before you are permitted to consult any similar manuscript in any European or American library (if you are allowed at all to do so without a research permit).
Deliberate mistake: In the link between the movie reel and nightclub scenes a train goes past. While the sound effect is convincing, the video has been reversed. The headlights on the train give it away, but cars under the bridge are also seen in reverse. (00:27:55)
Factual error: In the part where the two girls are chatting using Apple's iChat, which is another form of AIM, they are using a service supported by Apple called Bonjour. Bonjour is a network discovery technology developed by Apple, Inc. It allows computers and printers to automatically find and connect to each other's services using a new communication protocol, saving time and simplifying tasks such as file sharing and setting up printers. This would mean the girls would have to be very close to each other to use it, and obviously they weren't. (00:35:00)