Marge vs. the Monorail - S4-E12
Audio problem: When Mr Lanley is playing the piano, he plays some chords with both hands. During the line "Put up your hands and raise your voice", he plays the same chords, but at a different note, with only one hand.
Marge vs. the Monorail - S4-E12
Plot hole: When Homer is trying to stop the Monorail, he grabs the big M from the side of the train and uses it as an anchor. However, when the M cuts through 'Springfield's Oldest Tree', there is no visible monorail track or supporting pole in the background.
Marge vs. the Monorail - S4-E12
Continuity mistake: The Springfield forest is across the road from the school, but in many other episodes, it is somewhere completely different.
Marge vs. the Monorail - S4-E12
Continuity mistake: Mayor Quimby's suit changes from dark blue to purple throughout the whole town hall scene.
Marge vs. the Monorail - S4-E12
Continuity mistake: Throughout the whole town hall scene, people constantly change positions between shots.
Marge vs. the Monorail - S4-E12
Continuity mistake: When celebrities are coming to ride the monorail, the positions of people in the crowd changes positions between shots.
Marge vs. the Monorail - S4-E12
Continuity mistake: Doctor Hibbert was among the passengers on the monorail on the first ride, but he is seen with a pair of conjoined twins in his office soon after.
Continuity mistake: When Bart and Lisa wake Homer and Marge up in the morning of the Duff Gardens visit, the kids are standing by the bed. However, when Marge throws the mouldy sandwich in the bin in the next shot and Homer collapses, the kids have disappeared. In the next shot, they are back again.
Continuity mistake: When the police talk about the bumper cars getting stolen by Jimbo Jones, you see him and his 2 friends riding off in bumper cars. From the side angle, there are 2 blue and 1 red car, but from the rear view, there is 1 blue, l red, and 1 green car.
Continuity mistake: In this episode Hans Moleman's skin colour is yellow. However in "Duffless " his skin colour is brown and in other episodes it is a dark yellow-green colour.
Continuity mistake: When Selma is on video at the end of the episode, the iguanas's eyes change from yellow to white during the scene, but not between shots.
Factual error: When Selma throws Moleman out of her car, the passenger door is hinged at the rear instead of The Front as it should be on a relatively-modern hatchback, and the window crank is visible on the outside of the door.
Brother From the Same Planet - S4-E14
Continuity mistake: After Pepi and Tom walk off into the sunset together it cuts to Bart handing Homer another beer, and the picture behind the couch has brown sails over the boat, but next shot it's colored properly with white sails. (00:21:30)
Brother From the Same Planet - S4-E14
Continuity mistake: When Homer is showing Pepi the garage, it is purple. In the main titles and in every other episode, it is an orangey colour.
Brother From the Same Planet - S4-E14
Revealing mistake: The shot of Homer saying "Marge, when kids say bad these days, they mean good. And to shake your booty means to wiggle one's butt" is recycled from the opening scene from Life on the Fast Lane. Notice the animation is of a much lower standard than the rest of the episode.
I Love Lisa - S4-E15
Continuity mistake: When Homer and Bart are watching a clip of Sideshow Mel on wowee sauce and Bart then says "I'd give anything to go to that show", he has nothing in his hand. The shot cuts to Homer and he then says "I'd sell my first born son" and then the shot cuts back to Bart. When the shot cuts back to Bart, a Buzz cola can has appeared in his hand out of nowhere. (00:08:20)
I Love Lisa - S4-E15
Other mistake: When Lisa and Ralph are swinging at the end, they are swinging outside the frame, but the swing is tied at the top of the inside of the frame.
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.
Last Exit to Springfield - S4-E17
Revealing mistake: When we see Lisa singing and playing the guitar for the second time, if you look to the right you can see a blue mark on the building that is behind her (On the middle turquoise stripe). It appears and disappears twice.
