Continuity mistake: Watch kid drive Norman's power boat. He is at the steering wheel, and appears at the left and right side of the boat in the same scene.
Continuity mistake: When the boy is dropped off at the cabin, Ethel's sweater is zipped down. It goes to a close-up of her and the zipper is up. In the next shot, the zipper is down again.
Continuity mistake: When Norman is helping his wife uncover the furniture in the summer cabin, she hands him some sloppily rolled up sheets that drag the floor. The camera never leaves them, but for a few moments it zooms in and you don't see below their waists. When the camera zooms out again, the sheets in Norman's arms are all neatly rolled up.