Continuity mistake: When Claire is in the tub after Norman gives her a drug to immobilise her, she stops the hot water valve with her toe, although Norman opened the cold water valve.
Suggested correction: He explained that the water was too cold (he laid in cold water after faking his electrocution) and thus turned on the hot water. But when she turned the water off with the shower hose, the tap turned anti clockwise, so actually opened the tap more.