Continuity mistake: When Nell is in the study, the photo album of Crane opens. It then nearly falls so she grabs it. As she grabs it you can see the page has a picture on it, of two people's face very close up. But in the next closeup of the same page, the picture has changed and it is now Crane standing alone in the centre of the picture.
Continuity mistake: When Nell opens the ledger, it shows the first page. Two people are crossed out in the ledger. In between the rows which have been crossed out, there are ten rows of recorded people, which aren't crossed out. Nell then puts the ledger on her lap, and is still on the same page. Yet when it shows the page again, there are now only five rows in between the two crossed out ones.
Continuity mistake: Luke's hair changes length and style throughout the film. It starts off quite long at the back and sides over his ears then after Nell and Theo hear noises on the first night and Luke comes to the door to see what's happening its been cut, coloured and layered then when he's speaking to Liam Neeson a bit later on it's long again.