I think subtlety is lost in today's fast food world, so unlike my last The Shining gif, I'll tell you the secret up front because nobody got the last answer right. Ullman is sitting perfectly still, the room is pulsating. Don't tell me it's a flaw in the film. The shot just before this has Jack sitting perfectly still and the room around him is very stable. This room appears to be having a small earthquake, or maybe the hotel is alive and breathing. Also, the desk is on it's very own "Dutch Angle", because it's not level, but the table behind Ullman is level and so is the window. So, the desk is out of whack.