(at around 56 mins) During the séance, as Aurora regresses into a trance, her arms slip off the arms of the chair on which she is sitting. The next shot of her, looking from the other direction, shows her arms still resting on the chair again.
(at around 46 mins) When Laura is watching the old films, when we see one of the shots of Tomás, his eye hole is on the wrong side. In the next shot, it is on the right side again.
In the film, we see the lighthouse shining directly on the orphanage. In reality, coastal lighthouses are shielded so their light does not shine on land.
(at around 1h 27 mins) Simón enters the basement from the same door as his mother. It may appear the door was held closed by the wallpaper, and it would have been necessary to rip it apart in order to open the door but, if seen carefully, the wallpaper was tidily cut at the door's edges so it could work normally. Laura tears a bit of the wallpaper, but only for her search purposes.
(at around 19 mins) After Laura is in the shed outside the house and she finds Benigna hiding with a shovel, and after Laura then tells Carlos to come down and check again with her, Carlos' torch shines onto the camera several times, and the reflection of the camera and the torch is in the background on the window.
(at around 45 mins) Pilar describes the old home movie that Laura views as 8mm, but when we see the projector, the film is actually 16mm.