Revealing mistake: Gracie hugs the Russian waitress in order to have a better view of the disc hand-off appear on the monitor. As she raises her left hand that holds the book/camera lens, we see that the digital feed that appears on the monitor stays steady and level, even though she is raising the book/camera lens higher and closer to her face. Obviously the feed that we see on the monitor is not taken from the book/camera lens. (00:04:10)Super Grover
Visible crew/equipment: In the scene after Patrick Bateman's second encounter with the detective in his office, we see Bateman having sex at Courtney's apartment. After he rolls off her, Bateman approaches the large, stand-up mirror in the bedroom. In the upper right hand corner of the mirror, a boom microphone can clearly be seen moving around to pick up Christian Bale's lines. The next time we get the same long shot, the microphone is gone. (00:52:45)
Character mistake: At the memorial service the principal says that it's been 39 days since 39 loved ones had died. But there were 40 students on the plane and 4 chaperones, making the total 44. Now 7 people got off the plane which means 37 people related to that memorial service actually died, not 39. Two pilots would make up the numbers, but there would be flight crew too, which still leaves the numbers off.
Continuity mistake: In the scene in which Leonard writes on the back of his picture of Teddy, "He is the one. Kill him," we see a shot of Leonard placing the picture on top of his tan jacket on the bed as he goes to write on it. Then, it goes to a close-up of the picture in which the jacket has disappeared and the picture is lying directly on the blue bedspread. It actually happens twice within that same scene. (00:15:15)
Continuity mistake: When Harrison Ford is watching his wife laying in the bathtub ready to drown, the camera shoots her head several times between cutaways to Ford and the running water. Watch her head relative to the top of the tub in the various shots. In some her head is much higher than in others yet her body never moves.
Other mistake: Mr. Gellar never ages. We see a flashback of him when he kills Sarah's Dad when Sarah was a little girl. When Sarah is a detective, he still looks the same.