Bart vs. Lisa vs. the Third Grade - S14-E3
Continuity mistake: When we first see Willie standing by the Black Wall of field trips, the latest entry is at Willie's eye level. But when the angle changes, there are a lot more names on the wall, making the last entry appear just by Willie's chest.
Bart vs. Lisa vs. the Third Grade - S14-E3
Audio problem: When the third graders get on the bus, Otto says "pukers in back", but his mouth is open and his lips don't move.
Large Marge - S14-E4
Factual error: In Luigi's, the lobsters in the tank are bright red. They are actually quite dark brown until they are boiled when they become red/pink.
Large Marge - S14-E4
Continuity mistake: After Homer paints "El Homo" on the wall, he paints over it so that none of the letters are visible. In the next shot a couple of the letters are visible, and are only struck out with one line.
Large Marge - S14-E4
Continuity mistake: In some shots, the incorrectly-colored lobsters have their claws taped shut, and in others they don't. It's completely random.
Continuity mistake: When Homer bangs on the screen in the testing booth, the little sign on the top left of the glass that was there earlier is no longer there.
Continuity mistake: The house is ripped from its foundations, but later on when it falls down the waterfall you can see the floor is completely intact.
Continuity mistake: After the Simpsons are selected for the 1895 reality show, they're shown the video confessional room, with the only tech in the house. When Marge is in this room confessing about her blue hair, the doorknob is on the right, but when Bart is inside confessing that he's miserable, the doorknob is on the left side of the door.
Continuity mistake: When Homer brings his family to Lenny's apartment, as Lenny shuts his front door, its doorknob is on the right, but when Homer and his family depart Lenny's crazy apartment, now that front door opens the opposite way, with its doorknob on the left.
The Great Louse Detective - S14-E6
Continuity mistake: When Homer and Sideshow Bob are chasing the mechanic on stilts, the mechanic tries to get away, and his cape falls off while he is being chased. In the next shot, we see a close-up of the mechanic, and you can see his red cape is back on again. Then in the next shot, we see Homer and Bob chasing him, and his cape is off.
The Great Louse Detective - S14-E6
Continuity mistake: When we see the picture collage of Moe with the pickle jar the bottom picture is of them in front of the pyramids. When it pans around the pictures though, it turns into a picture of them on the beach.
The Great Louse Detective - S14-E6
Continuity mistake: When Bob pins Bart onto the wall in the final scene, his pajama top is stretched up so you can see his stomach. It then zooms in slightly when he looks at his watch and his stomach is covered.
The Great Louse Detective - S14-E6
Continuity mistake: Frank Grimes' gravestone appears to look different from "Homer's Enemy" and "Alone Again, Natura Diddly."
Special Edna (a.k.a. Love and Marking) - S14-E7
Deliberate mistake: When Bart and Edna are watching "Holes" in the IMAX theater, Edna sighs and pulls out a locket which we can see the back of. After opening it up to reveal pictures of her and Seymour, we find out its actually a triptych when she opens up another image of Seymour's mother. From the way she unfolds this extra picture, Seymour's mother would have had to be facing outwards, but in the previous shot the back of the locket was blank.
Special Edna (a.k.a. Love and Marking) - S14-E7
Factual error: During the video screening at the Teacher of the Year committee, the panel is watching the teacher who acts like Robin Williams. In the video the main judge says "Next" and pushes a button on the video control. It goes to the video that Bart Simpson sent in. How was this possible? The video control would only fast forward the video and two separate entries would not be sent in on the same tape. The committee wouldn't have spliced the footage together onto the same tape as the tapes were piled up on the desk. At the start of the scene one of the judges mentions to put in the next tape.
The Dad Who Knew Too Little - S14-E8
Other mistake: When Bart flashes Lisa's laser at Principle Skinner's bottom, Chief Wiggum can still see it even when his car is in the way.
Strong Arms of the Ma - S14-E9
Audio problem: The speech does not match the lip movements from when Bart says, "dad, do you plan to get in shape?" until Lisa says, "Uh guys, mom just left the basement." (00:12:17)
Strong Arms of the Ma - S14-E9
Audio problem: When the piano is playing Fur Elise, the keys do not move.
Strong Arms of the Ma - S14-E9
Audio problem: When Marge sprays the pepper spray at Ralph, the line she says after does not match her mouth.
Strong Arms of the Ma - S14-E9
Audio problem: When Homer says he'll eat twice as much, Bart says excellent, but that doesn't match his mouth.
Answer: I'm not sure if this is the one you're thinking of, but an episode of "Ray Bradbury Theatre," called "A Sound of Thunder," dealt with a similar matter: a group of hunters travel back in time to hunt dinosaurs, only to find things have changed when they get back because someone stepped on a butterfly.
Xofer