Factual error: In the scene where they are in the U.K, a little boy is hit by a van and you can hear the police and medical services coming. The sirens are American sirens which differ greatly from the High Low pitch that the U.k Is famous for and do not fit the scene at all.
Revealing mistake: At the book fair, Marcus briefly pauses to listen to Derek Jacobi's book reading. When he walks away, the camera follows an extra to her seat. If you watch when she enters the scene from behind the sign, the extra hesitates until the actor playing Marcus walks away, which is apparently her cue. (01:43:45)