In "Ghost," we see that Sam has learned how to manipulate objects in the physical world. But near the end, when Oda Mae comes to Molly's apartment to run from Carl, we see her begging Molly to unlock and open the door, even though Sam is right there in the apartment at the door with Molly. He could have just used his powers to unlock it, but instead asks Oda Mae for a penny to demonstrate to Molly that he is there and get her to open the door.
I always thought he didn't unlock it because he didn't want to overwhelm her or freak her out, but the penny does that anyway.
Any thoughts are welcome, and please feel free to correct any etiquette mistakes I make.