In book 3, episode 8 "The Puppermaster", when Aang, sokka, and Toph are questioning Old Man Ding about the spirit that controls people, notice the window he was preparing to board up. Throughout the scene, the number of boards change from 3, to 2, to 1, to none at all. Also, their positions change. They could be covering all of the window, half of the window, or none are covering the window at all.