Continuity mistake: When Rosemary has decided to sneak over to the Castevet's, she removes the towels from the closet shelves. She then tries to shut the door by pushing the towels (on the floor) into the closet. We see that the closet door does NOT shut all the way. Rosemary goes to get a knife, when she gets back to the closet, the door is completely shut, and she must now turn the knob to open it.
Trivia: The director, Roman Polanski, started the trend of an actor walking into a room and then going to the left, or right, and disappearing behind a wall and the audience when they first saw this shifted to their right, or left, so they could see around the corner. I don't think the director expected this but it did happen.