In reference to above posting, if you look closely you'll notice that as Diane moves toward the door...in the dark you can see that the cabinet is still in front of the door. The scene then cuts to Sam's reaction to her line of dialogue, and when the camera cuts back to Diane, as she turns on the light, the cabinet if back in its proper place. The assumption is that Diane moved the cabinet right before she turned on the light. We didn't see it because of the way the scene was edited. She moved it when the camera cut to Sam.