Continuity mistake: When Kirsty accidentally opens the box while in the hospital, the face with the large diamond design on it is initially on top, then when it cuts to a close up, the box somehow flips 90 degrees so the face with the circle on it is on top.
Continuity mistake: The amount of blood on Julia's face, neck and clothes changes from when she's inside the attic to when she goes out onto the landing, and then from when she then goes into the bathroom to wash herself clean. (00:38:05)
Revealing mistake: When Kirsty encounters the 'skinless' Frank, he says to her 'It's Uncle Frank' and you can see his left hand is normal and flesh covered, even though Frank is supposed to still be missing all the skin from his body. (00:58:10)
Continuity mistake: Throughout most of the film, Larry has a bandage on his right hand. When he talks to Julia through the bathroom door, Larry's bandage is on his left hand.