Question: What brand of pen did Oda Mae use and then ask the teller if she could keep it?
Question: After Willy takes Sam's wallet, why did Sam attack him? The scene happened so fast I can't figure out why.
Question: Was there any reason why the subway ghost was angry at Sam for being in the same train with him?
Question: Why did the angels only come for Sam after Carl dies?
Answer: They didn't - that was the second time they came for Sam. When he first died he started walking towards the light however when he saw Molly distraught he walked away (showing he had unfinished business on earth).
Answer: If the question is why did they wait to take Sam, we can only speculate. But as angels, they may have wanted to give him time to say goodbye.
Question: How did the hospital ghost, cemetery ghost and Subway ghost know that Sam was a ghost too?
Answer: New ghosts (such as Sam) apparently go through a learning process, exploring their abilities. Sam had to learn how to pass through solid objects, move solid objects, enter another human's body, etc. Obviously, the older ghosts had additionally learned to distinguish between the living and the dead.
Question: After the subway ghost shows Sam how to move things, he gets angry at Sam's question about his death, making him kick a cigarette dispenser. After kicking the dispenser, why does the subway ghost suddenly not recognize Sam?
Answer: The subway ghost was a paranoid schizophrenic who committed suicide by throwing himself in front of the train. As a ghost, he still has extreme mood swings that range from denial to grief to anger and even violence, and he apparently suffers short-term memory loss, as well.
The subway ghost told Sam that somebody had pushed him.
As I said, the subway ghost was a paranoid schizophrenic who is in denial. He insists that he was pushed; but his odd insistence implies that he actually committed suicide.
Question: If Carl is so terrified of being killed by the drug dealers after losing their money, why can't he simply leave the city?
Answer: Willy struck Molly (knocking her to the ground) when she tried to intervene, thus making Sam attack him in response. This fight led to Sam getting shot.