Norman Bates: A boy's best friend is his mother.
Norman Bates: Dirty night.
Milton Arbogast: We're always quickest to doubt people who have a reputation for being honest.
Norman Bates: We all go a little mad sometimes.
Milton Arbogast: Oh, someone has seen her, all right. Someone always sees a girl with $400,000.
Answer: What is shown is what you would see in the rearview mirror. Being in the mirror, it's a reverse image. Think about if you were looking at the cars pulled over head on/facing the driver, the road and the driver would be on your right. Shots in the mirror though shows the road and the driver on your left, the reverse.
Bishop73