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)
Factual error: At the very beginning, "Hereafter" makes the same factual mistake as was made in "2012" and "San Andreas": Crystal-clear tsunami flood waters. Of course, tsunami floods are always inky-black, filled with churned-up silt, sediment and debris.