Continuity mistake: When Bart falls down the stairs, you see him fall down at least 50 stairs in the close up. There are never this many on the full shots of the staircase.
Continuity mistake: When Homer and Barney are talking about the lottery, Barney says, "130 million." Then, they set their mugs on the table but when they all run off their mugs have disappeared. (00:01:50)
It's a Mad, Mad, Mad, Mad Marge - S11-E21
Continuity mistake: When Otto meets Becky at 'Der Crazy Kraut', there are a lot of children in the bus windows. However, just before he gives her the ring, the kids have now vanished.
The Boy Who Knew Too Much - S5-E20
Continuity mistake: Hans Moleman's clothes change from white to black during the trial. (00:12:05 - 00:13:25)
Oh, Brother, Where Are Thou? - S2-E15
Continuity mistake: When Herb, Bart and Lisa are watching Itchy and Scratchy, Herb goes from wearing a t-shirt and shorts to a shirt and tie between shots.
Last Exit to Springfield - S4-E17
Continuity mistake: When we see McBain at the beginning of the episode, after shooting some people, the magazine falls out of the machine gun. But from the next shot onwards it is back in the gun.
Continuity mistake: When Burns first shows the team the nerve tonic, the "&" on the 'Brain & Nerve Tonic' label is facing backward, but as Burns pulls it away it faces forward. Then as he moves it around as he's talking, the "&" switches between facing forward and facing backward again. This happens all in the one shot.
Continuity mistake: The shaving cream on Chief Wiggum's face disappears when Bart tries to confess about the phony kidnapping.
Other mistake: After the boxing match, the boys start "boo-ing" to the TV, and for a few frames Lewis goes from black to yellow, then to black, causing a flashing effect. (00:02:45)
Burns' Heir - S5-E18
Continuity mistake: The doughnut Homer later picks up isn't by the door when Lenny walks into Mr Burns' office, and we never see anyone put it there.
$pringfield (or How I Learned to Stop Worrying and Love Legalized Gambling) - S5-E10
Revealing mistake: At the dinner table Homer says something like "as you know it's always been my lifelong ambition to be a blackjack dealer." During this line, for some reason they appear to have used a clip from an older episode (Season 3 / Episode 3 - When Flanders Failed) and dubbed the line over. For one thing, the animation is of a much lower standard than the rest of the episode. And perhaps even more telling, when he says it, he is holding a fork with some food on it, but from the earlier shots we know there is no food in front of him.
Continuity mistake: When we first see the power sander, there is only a white patch on the side. In the next shot when we return to viewing it, "Property of Ned Flanders" has appeared.
Continuity mistake: After Bart is sent to Maison Derierre, he knocks on the door. Belle answers it and for a couple of frames her arm is naked. Then suddenly her corset appears on her arm.
The Springfield Files - S8-E10
Continuity mistake: At the kitchen table, when Homer talks about getting mocked on his own birthday, they're eating breakfast. But when Marge, Lisa, Bart and Maggie all go to pet Santa's Little Helper, the breakfast has vanished.
Continuity mistake: All through out the episode, Bart draws his pictures with only one pencil, but they all end up in color when he's done.
Simpsons Spin-off Showcase - S8-E24
Continuity mistake: In Moe's spin-off, just before Barney leaves the bar, his beer glass vanishes.
Burns Verkaufen der Kraftwerk - S3-E11
Continuity mistake: Before Horst wants to talk with Homer, Lenny is standing beside the donut box, who wasn't seen in the shots before and after. (00:12:15)
Burns Verkaufen der Kraftwerk - S3-E11
Continuity mistake: In the parking lot, when Carl arrives, he is wearing a blue tuxedo. It changes to a lighter blue, and then back to its normal color when he gets in the car. (00:07:05)
Continuity mistake: When Bart and Lisa are looking at the globe, Bart points out Argentina and 'Ran McNally.' 1) Next time you see the globe, it is showing Africa and Asia 2) Asia is shown incorrectly and 3) The equator has disappeared.
Skinner's Sense of Snow - S12-E8
Factual error: Superintendents are the ones who decide whether or not schools should be closed for snow days, not school principals.