Okay, I saw this slipup in the Episode with the Carnival people (Carnis). After the Cooters make Homer and Bart in charge of the ring toss game, Bart cons Skinner and his mother to try the game. Skinner attemps to get a lamp and obviously loses. At this point we can tell that 3 items go in this order (from left to right) knife, magic 8 ball, and then the lamp he was trying to get. After numerous attemps at the lamp, Skinner's mother calls him a failure. He then proceeds to try and throw at the knife. They show us the angle of him throwing from behind the items on the shelf. Now we can tell that the 8- ball has disappeared! I guess it really is magic!