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)
Psycho IV: The Beginning (1990)
1 continuity mistake
Directed by: Mick Garris
Starring: Henry Thomas, Anthony Perkins, Olivia Hussey, CCH Pounder
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.
Mother: Get that whore out of my house.
Young Norman Bates: She's not a whore, mother.
Mother: I said get rid of her. Or do I have to do it myself?
Young Norman Bates: No, Mother. I'll get rid of her.
Mother: Kill her.
Young Norman Bates: Kill her? I can't! No! No, I can't.
Mother: Alright. Alright. Then I'll do it for you.
More questions & answers from Psycho IV: The Beginning
Answer: Norman is mentally stable in this film. Connie and Norman fell in love during his institutionalization. After being deemed sane and released, they were married. Norman is afraid to have children because he doesn't want to pass on his psychosis. Connie believes that with proper care, their child won't end up like Norman, and plans to become pregnant.