When Wendy annoys Jack while he's working (bringing to his attention the weather report) between "What do you want me to do about it" and "I'm not being grouchy" suddenly from out of nowhere a chair appears behind Nicholson. Maybe the hotel was indeed haunted???
"In the scene where Jack is writing and gets mightily upset when Wendy interrupts him, watch the chair behind Jack. It vanishes and then reappears. This was, however, intentional from Kubrick. The audience was supposed to get a subconcious feeling that something was wrong. Nice touch."