The Bonfire Of The Manatees - S17-E1
Factual error: Alec Baldwin, as an expert on manatees, says that they are also called dugongs. Manatees are found in Atlantic coastal waters and in the Amazon and tributaries. The dugong is a distinct species found in the coastal waters of the Indian and southwest Pacific oceans.
Factual error: During the theme, the Simpsons' mailbox flag is on the wrong side of the mailbox. (Flags are always on a mailbox's right side, when viewed from The Front. The one at the Simpson home is on the left side of their mailbox). (00:01:45)
Factual error: Moe has a double barrelled shotgun that fires four times. A double barrelled shotgun can only fire two shells before having to reload.
Factual error: The cover of "World's Finest Comics" #94 is shown on the wall at the comic book store. It features Superman with a sign that says, "Gotham or Bust," and Batman gulping. The actual cover of "World's Finest Comics" #94 shows Superman being sprayed with liquid kryptonite while Batman and Robin catch sight of him.
Factual error: After Bart's prank call with Moe, you can see Bart and Lisa laughing. However the telephone's wire does not connect to the receiver. (00:09:40)
The City of New York vs. Homer Simpson - S9-E1
Factual error: The windows of the World Trade Center couldn't open and the Twin Towers weren't in front of each other as depicted in this episode. They were at an angle.
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.
Factual error: When Rod and Todd Flanders are roasting marshmallows in the car, Todd's marshmallow was the only one above the lighter, even though both of them have turned black. (00:17:40)
Factual error: When you see Ned Flanders put the earth back inside the hole, he puts it back in much faster than is possible. In one shot, he is only just starting to put it back in, then you see Bart who talks to himself for a few seconds, then back to Flanders, who has finished burying what is later to be revealed as the plant that he (Ned) drowned.
Kamp Krusty - S4-E1
Factual error: In the last scene, with the picture of the bus leaving Tijuana, it says "Leaving Tijuana" above the gate leading into the city.
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.
Factual error: When Bart declares war on Nelson, Herman uses the declaration from the Franco-Prussian war and puts "Bart" in place of "Otto Von Bismarck". The thing is, Bismarck didn't declare the Franco-Prussian War, Napoleon III of France did. A small error, maybe, but something that a war buff like Herman should know.
Margical History Tour - S15-E11
Factual error: Lisa, as Salieri, says she has wine for sale : "Claret, Port, Riesling ...". All three glasses on her tray are filled with red wine. Riesling is a white wine.
Tree House of Horror VI - S7-E6
Factual error: In "Nightmare On Evergreen Terrace", Martin has a dream, in which he speaks Latin. At one point, he says a verb that doesn't exist: "morire". The words is "mori" (to die), "moritur" (noun dies) or "moreris" (you die). The "moirie" is also on the blackboard behind Martin. (00:08:20)
The Fat and the Furriest - S15-E5
Factual error: Homer creates a giant sugar ball by making a normal sized cotton candy on a paper cone, and then coating it with liquid caramel. The cotton candy holds its shape and Homer continues to expand it with more cotton candy and caramel. However, cotton candy dissolves very quickly and tears apart easily. Between the weight and moisture content of the caramel, the original cotton candy would have immediately melted and/or collapsed.
The Boy Who Knew Too Much - S5-E20
Factual error: Apu (an immigrant from India) could not have been selected for the jury because he is not an American citizen, and this was before he became a naturalized citizen in "Much Apu About Nothing".
Factual error: In the episode with Donny, when Bart sees principle Skinner go into the school to meet with the rat, the door is backwards. The bars that are pushed in to open a door are always on the inside.
Factual error: When Bart is trying to escape from the girls at the start, Bart's door opens into the room. This would mean the hinges would be inside Bart's room and the girls couldn't have been able to remove them.
Tree House of Horror VI - S7-E6
Factual error: During the "Attack of the 50 ft. Eye Sores" segment, the family steps into the footprint of the giant donut guy to look at the label. The label should appear to be spelled backwards, but it was not.
The Ziff Who Came to Dinner - S15-E14
Factual error: When the SEC guys break up the poker game they arm their guns in the same manner you would with a shotgun (there is even the shotgun cocking sound effect) yet they are M-16 style weapons and would not need to be armed this way.
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