"Pull" joke

A blonde kept having the same weird dream everyday, so she went to her doctor.
Doctor: What was your dream about?
Blonde: I was being chase by a vampire!
Doctor: (giggles quitely) So... what was the scenery like?
Blonde: I was running in a hall way.
Doctor: Then what happened?
Blonde: Well that's the weird thing. In every single dream, the same thing happened. I always came to this door, but I couldn't open it. I kept pushing the door and pushing the door, but it wouldn't budge!
Doctor: Did the door have any letters on it?
Blonde: Yes it did.
Doctor: And what did these letter spell?
Blonde: It said "Pull"