Revealing mistake: When young Norman Bates is spying through the peephole on his mother, who has brought home a man to the motel, we see him in the shower. Although the curtain is translucent, we can see he is wearing a black speedo.
Deliberate mistake: In the whole of the 'Psycho' series, there has never been a closet door next to the dress cabinet in Mother's room, but for this movie there is suddenly a closet.
Continuity mistake: Norman pours poison into the pitcher of iced tea. In the next shot, we see him carrying the pitcher and two full glasses on a tray - but the level of liquid in the pitcher hasn't changed, even though he's supposedly filled the glasses from it. Later, when the pitcher is sitting on Mother's dresser, the pitcher's level is lower, but no one has poured anything from it. (01:00:05)
