Deliberate mistake: Lou and Eddie are driving Bart around in the cop car. Bart asks when they're going to shoot people. The shot cuts to Lou, who is driving. The entire frame of the car disappears around him and it's just him superimposed over a background. The shot cuts again and the frame is now visible. Even if it was a low-angle shot, you'd still see the roof of the car.
The Simpsons (1989)
1 deliberate mistake in Separate Vocations - chronological order
Continuity mistake: When Homer's Vegas wife shows him the video in front of Marge, it shows Homer kissing Ned. This didn't happen when she showed it in the Vegas episode.
Homer's brain: It's simple, just use reverse psychology.
Homer: Reverse psychology? That sounds too complicated.
Homer's brain: Alright, don't use reverse psychology.
Homer: Alright, I will!
Trivia: The Simpsons holds the record for most guest stars; it is also the only non-variety show to have had appearances from three former Beatles (Paul, George and Ringo).
Question: Which episodes feature the "Howling Dog" (usually used on outside shots of buildings)?