Corrected entry: In "Bart's Comet", it was shown that the only way out of Springfield was a bridge across a circular gorge. Yet, in this episode, there is an easy access border between Springfield and Shelbyville.
Corrected entry: Sheri and Teri are the same height as Bart and Lisa, yet in the opening they sit beside Lisa in the orchestra and they are huge - almost twice the size of her.
Correction: Actually, they seem to be the right size.
Corrected entry: Lisa says that Jebediah Springfield is indeed Han Sprungfeld because there's no record of Jebediah Springfield before 1795. Yet in "Whacking Day", Bart mentions that there is a historical record of Jebediah Springfield serving in the Battle of Ticonderoga in 1777.
Correction: Thats essentially the point. Much of Jebediah's records at times seems to be generally more made up than fact, as evidenced in the film at the start of the show in which he managed to tame a wild buffalo with his bare hands! Yet concedes it was already tamed he merely shot it. While Bart's history book might claim to say he served in the Battle of Ticonderoga, Lisa's books and the statement she found in his fife contradicts that point. In her book it claimed that in 1780 he fought George Washington. After this he wrote his confession on the piece of the painting of Washington he ripped off and stole. Then he hid the confession in his fife. Essentially the statement found from the George Washington painting told the real truth and his silver tongue backed up the statement.
The Simpson's 138th Show Spectacular - S7-E10
Corrected entry: During the "Who Shot Mr. Burns" alternate ending with Smithers shooting Mr.Burns, Smithers is smartly dressed and wearing his jacket. At the end of part 1 and start of part 2, Smithers was badly dressed. Carl also points out at the end of part 1, that Smithers left his jacket on his chair after The Town hall meeting.
Correction: As pointed out in the episode, the sequence was only filmed to keep the secret of who was the shooter from being leaked by the staff of the show. As pointed out, the DNA evidence in the episode would have to be ignored which proves the creators were never concerned about continuity as the sequence would have been unusable. In addition as pointed out on the site, deleted scenes or alternate sequences cannot be considered mistakes to the final cut.
Corrected entry: Creator Matt Groening's initals were initially in Homer Simpson's hair and ear from the side. Matt Groening says himself (in one of the Simpsons comic book specials) that he changed it because it would be too distracting if the secret ever got out. He also says that he puts them in now only when he is drawing pictures for fans.
And Maggie Makes Three - S6-E13
Corrected entry: After Homer gets his job back at the plant and returns home to complain to a pregnant Marge about how much he hates his life, a picture of Maggie can be seen hanging on the wall behind the couch - despite the fact that Maggie hasn't been born yet.
Tree House of Horror III: The Simpson's Halloween Special III - S4-E5
Corrected entry: When Homer says that he is going to get Bart a birthday present, he runs to the car and drives away. Not only is it impossible for him to run out to the car, get inside, start the engine and drive away in the time he did, but he presumably used the back door (as we did not see him use The Front door). Why didn't he use The Front door? It would have been much quicker.
Correction: Matt Groening (the creator) has said that they decided to do an inside joke in the show of characters driving away too quickly, so when Homer does it, it is on purpose.
Corrected entry: Marge's real hair color changes throughout the show. There are some episodes that show her hair is naturally blue, such as ones with flashbacks that show her as a child or younger teen with blue hair. Other episodes indicate that her hair is really brown, but she dyes it.
Tree House of Horror II: A Simpsons Halloween - S3-E7
Corrected entry: As Maggie makes her wish, the wall color in the room changes from pink to green. (00:03:50)
Correction: The only shot with a green background is that of the actual paw, and it's an overhead view showing a green floor. The wall colour never changes.
Who Shot Mr. Burns? (2) - S7-E1
Corrected entry: The Police and Smithers go to the Retirement Castle to question the old man about Smithers shooting him in the boot; this would be very difficult seeing as the retirement castle was destroyed in Part 1.
Correction: We've seen on countless occasions that the retirement home is a very poorly kept one. We also know the old folks are stubborn there. Just because it split in half probably wouldn't be enough to make most of them move out. It wasn't entirely destroyed in part one, just split and at an angle.
Corrected entry: The person Homer tries to prank with the bucket of cement is a different person to the one he ran over 5 years ago.
Correction: That actually makes a lot of sense, it being a different person. When Homer ran the dean over, he caused pretty serious damage (he was in a full body cast). A paralyzed dean probably wouldn't be able to do his job, and since he re-admitted the students who were expelled the board had a go-ahead to fire him.
Corrected entry: How can Mr. Burns dance so well? On several previous occasions it has been made obvious that he is weak and feeble.
Correction: Burns is more weak when it comes to strength, i.e. lifting or moving items even ones that are particularly light. Something like walking and dancing is not as much of a problem. He also has danced before. In the episode "Hunka Hunka Burns in Love" he managed to dance (with some assistance from an oxygen tank in his jacket pocket).
The Springfield Files - S8-E10
Corrected entry: After Homer comes in contact with the alien and he's reporting the sighting to Police Chief Wiggum, he says "And the alien appears every friday night." How could he know that if he only saw the alien once?
Correction: Homer doesn't know this; he is just making a very rash assumption about the alien sightings.
One Fish, Two Fish, Blowfish, Blue Fish - S2-E11
Corrected entry: At the start of the episode, you see the meatloaf inside a metal tin in the microwave. Heat waves reflect off metal, so the microwave should have been blown up.
Correction: Putting metal in a microwave doesn't make it blow up, it just creates sparks everywhere.
Corrected entry: Bart's cell phone has 9 buttons. Real phones have 12 buttons.
Correction: There are phones for children where the numbers are preprogammed by parents so they can't just call anyone. These don't have 12 buttons.
Corrected entry: When Red is declared the winner of the eating contest and dies, just before he is pronouced dead by Dr. Hibbert he blinks. Last time I checked dead people don't blink.
Correction: He blinks and then is pronounced dead, seems OK to me. If it happened the other way round then it's a mistake.
Corrected entry: In this episode Dr. Hibbert says the crayon was never spotted because he always covered it with his thumb, but in episode 4-18, "So It's Come to This: A Simpson's Clip Show", when Homer is in the hospital, his head X-ray is placed up on the light box on the wall, and is visible with nothing blocking it, so the crayon should have been spotted then.
Correction: The joke in the scene is that there really is no way to explain why or how he would miss a large crayon in Homer's brain after all these years, numerous injuries and many x-rays. Even if he should have seen it, its a character mistake. As you pointed out there was no way he should have missed it but either he really did miss it everytime or is lying to cover up his mistake.
Corrected entry: When Selma is in the bath with a cigarette, she sinks under the water dragging the cigarette with her. However, if you look and listen very closely, the sound of the cigarette being extinguished happens very slightly before it actually makes contact with the water.
Correction: In the shot as she is just about to go under the water, you can see the cigarette start to glow a bit redder. This would mean Selma is inhaling as she is going under the water. As she would be inhaling, a small area below the lit area would start to get hotter and so would make sense that the sound of it being extinguished just a split second before the lit area goes under the water.
Tree House of Horror XII - S13-E1
Corrected entry: In the leprechaun short episode, a lot of things attend the wedding, including Kang and Kodos, the space aliens. One of Kang/Kodos starts crying and says: "I always secrete ocular fluid at weddings." Yet, in another clip episode, the space aliens invade Homer's Roasting Hour. Lisa thinks they're crying, but they say that they are vomiting from their eyes. Yet, in this episode, one of them starts to cry.
Correction: The key words here are "they say". We have no idea if they are telling the truth or if they are crying when they tell this to Lisa. Besides this, we also have no idea about how the bodies of the aliens work. It could be that both their crying AND their vomiting takes place through the same channels (the tearducts).
Gump Roast - S13-E17
Corrected entry: When Homer starts to remember all the memories he has had with the Simpson family car, one of the clips is actually from an episode in which Homer was stealing Moe's car which isn't the family car.
Correction: The geography of Springfield changes often; sometimes it is seaside, sometimes landlocked, sometimes it is a small town, or as big as New York City, or exactly the shape of Texas. This is a pretty obvious gag and therefore not a mistake.