At one point a telephone bell is heard ringing somewhere in the house but, when the woman finds the source, it's a Trimphone. Trimphones do not ring with a conventional bell sound but have a distinctive chirping tone.
The part in the film where the mother and children try to escape the house and get into the car, the mum realizes that she left the keys inside, where her possessed husband is. When she runs in the house and tries to get her keys, she is sat at her husband's feet on the edge of the bed and a member of crew dressed in black can be seen to the left of the husband.
When she cannot open the door to Penny's room, Meg tells Penny that she does not have a key. However, when they are talking about the incident later, Meg says that there is no key for the door.
Meg discovers a hidden passageway in the house of which she has no prior knowledge. However, as a renovator, she would need to have detailed knowledge of the building plans. In fact, even the man who initially agrees to help her is aware of the passageway while she is not.
While Meg is trying to break down the bricked up passageway through to the root cellar in order to find Harper, Penny falls into the root cellar via an open doorway in the floor outside the main entrance. Therefore, if Meg wants to reach Harper, all she has to do is enter through that doorway, meaning her smashing of the wall makes no sense.