Continuity mistake: In the very beginning, Fool falls down the basement stairs when the man pulls the lever to make the stairs a ramp. He is wearing a purple and black striped shirt. Later, near the end, Fool goes back into the basement on the same stairs. This time, he is wearing a green shirt. When the man chases him and pulls the lever again, we see the same footage of Fool rolling down the stairs/ramp from earlier (black & purple shirt). When Fool gets back on his feet, his shirt is green again.
Continuity mistake: When the third Person from Under the Stairs bursts out (from the wall) the Woman is flinching in the corner, pressing up against the wall. As she does she breaks the brown wooden panel in the wall behind her, splitting it in two. In the next shot the wall is back intact.
Factual error: When the cop (Bobby) asks the woman if it's her van, she says she found it when she got home. In actuality, the police would get suspicious because she didn't report it. Someone comes home and sees someone else's vehicle parked in their driveway and neither her or the man call to report it (at the very least to have it towed)?
Continuity mistake: When the Man and Woman have lost Alice, they look in the kitchen to find her, and the Woman starts opening up some cabinets and in the process she leaves some of the doors open. Then in the next shot, the cabinet doors that are open have now changed, and some doors that were open in the previous shot are now closed.
Continuity mistake: When the Man blasts the two doors away with his gun, the two outer doors get blasted off, however a large piece of plywood still remains in this entrance. In the next shot, when the Man yells "Gonna kill you!" the whole entrance is clear and the remaining wood is now gone.