Revealing mistake: Later into the film Roger realises that his aunt's paintings hold some significance to the whereabouts of his missing son. He removes a cloth from the top left of a painting revealing an image of his son trapped in his bathroom cabinet. Note the cabinet door is the wrong way round to the one in his bathroom.
Revealing mistake: While Roger is in the bathroom he hears banging, and when he opens the door he sees the gardening tools poised to attack, and in the shot from the bedroom facing Roger, we can see the stunt wires attached to the hedge shears as it hovers in front of the door's wood casing. (00:44:35)
Revealing mistake: About 27 or 28 minutes into the film, right before the giant creature flies out at Roger through the doorway, you can see the wall (part of a film set) "wobble" for about a half second as Roger opens the door.
Answer: That's the horror movie Don't Look in the Basement (1973), at its own timecode 01:09:30 within that movie.
Super Grover ★