Psycho

Dr. Fred Simon: Like I said... the mother... Now to understand it the way I understood it, hearing it from the mother... that is, from the mother half of Norman's mind... you have to go back ten years, to the time when Norman murdered his mother and her lover. Now he was already dangerously disturbed, had been ever since his father died. His mother was a clinging, demanding woman, and for years the two of them lived as if there was no one else in the world. Then she met a man... and it seemed to Norman that she 'threw him over' for this man. Now that pushed him over the line and he killed 'em both. Matricide is probably the most unbearable crime of all... most unbearable to the son who commits it. So he had to erase the crime, at least in his own mind. He stole her corpse. A weighted coffin was buried. He hid the body in the fruit cellar. Even treated it to keep it as well as it would keep. And that still wasn't enough. She was there! But she was a corpse. So he began to think and speak for her, give her half his time, so to speak. At times he could be both personalities, carry on conversations. At other times, the mother half took over completely. Now he was never all Norman, but he was often only mother. And because he was so pathologically jealous of her, he assumed that she was jealous of him. Therefore, if he felt a strong attraction to any other woman, the mother side of him would go wild.

[Points finger at Lila Crane]

Dr. Fred Simon: When he met your sister, he was touched by her... aroused by her. He wanted her. That set off the 'jealous mother' and 'mother killed the girl'! Now after the murder, Norman returned as if from a deep sleep. And like a dutiful son, covered up all traces of the crime he was convinced his mother had committed!