This is Sam stimming with books (the voice in the video is Maya who is a bit jealous because she wants to make a video too). He does this most of his waking hours when he is in the house. When he is out of the house he does the same action but with other objects. The resulting mess is maddening. The sound of books hitting the floor still makes me cringe. We make him "clean up" but it has no effect on the behavior.