The Resurrection of Joe November - S3-E24
Revealing mistake: Stock footage used for the Mardi Gras scenes shows a crowd dressed in 20th Century clothing.
Revealing mistake: After he's ambushed and killed in the alley, the "dead" sheriff can be seen breathing quite healthily.
The Devil's Necklace: Part 1 - S4-E31
Revealing mistake: Bart teaches Tawney how to wash her face with a bar of soap. When he dries her cheek, the actress' heavy "Indian" make-up is wiped away, revealing a very white complexion. The white patch disappears in the next shot. (00:45:00)