In the episode "Shiny teeth", watch when Timmy is getting Chip's teeth back. When Timmy is near the door, there is the start of a sign; "EX", probably exit. When Dr. Bender screams "Noooooooooo!!!!!!", the sign above the door says "No screaming" I know this was put there to add humour, but the Exit sign has disappeared!! Where did it go?