Revealing mistake: At the end where Katie kills Kristi by throwing her upwards into the camera mounted on the wall, the reflection of them both in the mirror behind them doesn't match their actual movements. In the reflection, Katie simply pushes Kristi against the wall. She doesn't throw her upwards.
Continuity mistake: During the last night Martine is working for the Rey family, she is shown saying prayers in the kitchen and TV rooms. During that time, the kitchen camera shot has knives, spices and a chopping board on the counter, but in the next kitchen shot, everything is replaced by a fruit bowl. You'll also notice that the hanging pots and pans change in number, order and colour and the flowers located on the table change variety and also too the bowl/vase.
Continuity mistake: When Martine hears noises in the house, she goes upstairs to get Hunter and then starts cleansing the house with incense. Before she goes upstairs, notice how the pots and pans hanging in the kitchen are different makes/colours when she come back downstairs with Hunter. They change again when Daniel and Kristi return home.
Continuity mistake: In the scenes where the baby is shown moving about the house opening doors, the nursery room door had been left open yet he is shown opening it. The basement door is shown as being opened and the next shot shown as closed. The timecode doesn't allow time for the ghost to have done anything, and without sound in the film.
Other mistake: We are seeing the movie as if we were watching recordings, that's why we see the surveillance camera shots as the device installed to change from one camera to another would let us. It takes very short time from one camera to another,but in some cases, as to follow things to happen, the shot stays in one angle (camera) for a longer period, not keeping the timing for the mentioned device.