Revealing mistake: In the pilot, the exterior of a bar is shown as a scene transition. While the show takes place in Los Angeles, the bar and street intersection shown are in Providence, Rhode Island. You can see a banner with the word Providence in the shot and the street names match the intersection.
Kreplach and a Tiny Tush - S3-E7
Revealing mistake: When Gill called Kristy she picked up, but if you look at her phone someone is still calling. (00:02:20)
God Bless Her Rotting Soul - S8-E3
Revealing mistake: If you look at Professor Youens' left foot when he is lying on the couch you will notice a chroma key error - half his foot is almost eaten by the carpet. (00:19:15)
Revealing mistake: During "Brand New Day", watch the background as Dr. Horrible appears as a giant and stomps down the city-street. As he takes his first step, a piece of concrete from building to his right falls off and hits the ground. However, if you look closely, it's obviously a quickly-made computer effect. As the piece of concrete hits the ground, it simply vanishes, and is replaced by a rather odd-looking animated "poof" of dust. The issue is the concrete piece was much bigger than the cloud of dust, so it's clear that the piece simply disappears right as the dust-poof appears.
Revealing mistake: When Johnny shows up to Cobra Kai dojo and all the kids are there. In the video playback they show on the phone you can see Miguel didn't land the kick, and the kid just fell down. (00:28:18)
Mark Hamill - S4-E16
Revealing mistake: When Luke Skywalker is introducing his 'cousin' Mark Hamill at the end, you can tell it's a split screen by the fact that Luke looks right past him, even once he's on stage. (00:25:10)
Psy vs. Psy - S2-E3
Revealing mistake: Whenever you see Shawn and Gus outside it appears to be warm but if you look in the background people are wearing jackets and heavy coats, revealing that during filming it was winter and cold out.
Revealing mistake: When someone suggests crying as a way to get the emperor out of Fry's body, he says 'that's a great idea', the emperor's face stays still on Fry's stomach, instead of moving in sync with Fry's body. (00:15:50)
Revealing mistake: When Fletcher and Godper are assigned to the work party and they get locked into the church, one of the prisoners, Melvin (the hippy) leans against one of the 'stone' pillars of the church, causing it to wobble.
Close Encounters of the Beans Kind - S3-E8
Revealing mistake: When Louis and Beans fall from the sky on the bike, if you look carefully, you will see that they're both dummies.
Revealing mistake: If you look at Les out of Les Alano's' drumming, several time throughout the whole show, you can see he is miming and his stick is not even close to the actual drum.
Revealing mistake: The crane in the garden is behind the tree, but we see just the top of it - and under it is nothing.
Revealing mistake: When Zack and Cody are tied up by the secret spy, when Cody is texting Bailey "Help Me" with his toes, you can see that the Mobile has a black screen, and is turned off. And he was just hitting random buttons with his toes.
Revealing mistake: In the episode with Fast Eddie McClintock, there are two revealing mistakes in the scene where Fast Eddie jumps the roadblock. First, the ramp he jumps off of is visible in numerous shots before he shows up. Second, explosive charges can be seen in the wheel wells of the police cars before they run over the spike strips.
Man-Eater of Surrey Green - S4-E11
Revealing mistake: When Steed and Mrs Peel are fighting one another, the stunt doubles used bear absolutely no resemblance to the actors.
Revealing mistake: Near the end when Randy is driving away with Harry you can see that the steering wheel doesn't move when Randy turns it.
Revealing mistake: When the school bus is shown cruising around the corner on the way to the camping area, you can see that as it turns the corner is is virtually empty. (01:38:50)
Revealing mistake: At the point where someone gets a small bruise on the upper arm, the crew are all in a pile and thrashing about on the floor. There are 5 pairs of legs instead of 4. Arthur is in his pajamas, Zaphod is in orange trousers, Trillion is lying on top of Ford and Ford is too far away for them to be his legs. [The fifth pair of legs belong to the person playing zaphod's third arm - doesn't mean it's not a mistake, but that's where they come from.]
Skating Away - S2-E2
Revealing mistake: When Van falls from the roof, you can see that the backdrop gets hit and starts to move.
How to Succeed in Farming Without Really Trying - S3-E6
Revealing mistake: When the patroon is policing the area, raking and sweeping, they are not really raking or sweeping. They are just going through the motions but the rake and brooms are not touching the ground. (00:06:00 - 00:07:00)