Corrected entry: When the kids are broadcasting townspeople's secrets, and everyone else is in the meeting, Lisa says "And guess who's been practising medicine without a licence?" - scene cut, then cut back to the sign - "That's right: Homer Simpson" immediately afterwards, "D'OH!" is heard. The kids are OBVIOUSLY at least 1.5 miles from the town hall, so there should have been a sound delay in between Lisa's last statement and hearing Homer's voice.
Corrected entry: This concerns when Bart is in the ghost town, watching the robotic can-can dancers. When the four dancers first come out and start their kicks, one loses a leg which goes flying out of the window, breaking it. However when the camera cuts back to the dancers they all have both their legs.