Was teaching in a classroom with ten kids, and the lights kinda reflect on the whiteboard and I can get a view of the kids. I was writing on the board, and saw one of the disruptive kids stand up and could hear the desk move. I immediately called out his name and said, "sit down". The students tell me that he's not in class yet, I turn around, and all the kids are shuffling to sit in the front and no one dares to look at the spot where he sits.
After class, one of the girls told me that whenever they use that classroom to study, they always hear that desk in the back of the class move and dark shadows around that general vicinity.