In the one episode where Spongebob convincing his grand-mom he's grown-up, near the end there is an incident you can catch if you really pay attention. Near the end when Spongebob is leaving his grand-mom's to go to work (he's feeling really sad). He slowly exits while the camera switches between Spongebob and Patrick with Bobby's grand-mom. Pay attention to the door, in one scene Spongebob is outside but his hand is inside (animation slip-up), and the knob is next to the door-hinges. It's a really messed up scene. It's not too big, but still look for it.