Treehouse of Horror XV - S16-E1
Continuity mistake: When Chief Wiggum has been caught, we see him drop his eel pie, then when the shot changes it is not there. (00:13:30)
Treehouse of Horror XV - S16-E1
Continuity mistake: When Comic Book Guy gets stabbed, we see him reaching for a potion, and in the first shot, its a purple liquid with no label on the bottle, and when the shot changes we see it is a green liquid with a label on the bottle. (00:10:20)
Home Away From Homer - S16-E20
Continuity mistake: As the Simpsons are in the cinema watching "Kosovo Autumn" you can see there is a seat next to Homer to the right of screen. When Homer starts complaining about the film but cannot leave because he is stuck in his seat, the shot changes and we see him from behind however the seat that was next to him has disappeared.
Continuity mistake: The lock only appears on the door when Marge uses it. (00:14:45)
Home Away From Homer - S16-E20
Continuity mistake: When Coach is cutting down trees he tells Homer that he borrowed some petrol (or 'gas' in America) from his car, and the shot goes to his car. However when Homer runs indoors the car has vanished.
Home Away From Homer - S16-E20
Continuity mistake: For "Home Away From Homer": Bart looks out his bedroom window and sees the college girls doing sexual actions in the Flanders' spare bedroom. But, there is never a window in Bart's room that could possibly face the Flanders' house. [Bart's window in many episodes does face Flander's house but in other episodes like "Bart's Friend Falls in Love" and "Bart the Mother" it faces the treehouse which is the backyard of the house.]
On A Clear Day I Can't See My Sister - S16-E11
Continuity mistake: For "On a Clear Day, I Can't See My Sister": Throughout the episode, the backyard alternates between having a fence at the end and a forest at the end.
Continuity mistake: When the two chinese guards are dragging Budda Homer along, in an overhead shot we see a desk, with one filing cabinet behind it. In the next shot, the guards stop to rest, and now there are two. (00:17:25)
Home Away From Homer - S16-E20
Continuity mistake: Ned's front door before he and his family leaves opens on the left side (when looking at it from outside), but after the "Coach" has moved in, it opens on the opposite side.
Home Away From Homer - S16-E20
Continuity mistake: When Homer tries to leave his seat in the cinema and complains about eating the apple, the shot shows his body fat has wedged him in the seat. However we can see from all the shots before this that the fat was never wedged in like it was when he was trying to leave.
Fat Man and Little Boy - S16-E5
Continuity mistake: When Bart is playing with his toys, we see that in one shot on the shelf there are 4 books, then in the next shot there are 5. (00:03:50)
Continuity mistake: After Selma gives Madam Wu the sack of ten thousand "happinesses" the sack instantly vanishes from off the table. (00:08:40)
There's Something About Marrying - S16-E10
Continuity mistake: Reverend Lovejoy is unable to cite which book in the Bible condemns homosexuality, but in "Homer the Heretic," he is able to recite, from memory, a completely random Bible verse.
Continuity mistake: When Cletus arrives, to get his child back from Selma, we see Lisa wearing purple gloves. In the following shots, as she speaks to Selma, her hands are bare. (00:04:40)
Continuity mistake: The hospital band on Selma's right wrist keeps appearing and disappearing after they watch the menstration video. (00:03:00)
She Used to Be My Girl - S16-E4
Continuity mistake: Lisa puts a statue of liberty head on it's side in her bed to make it look like she's in bed. But when Marge pulls back the covers the head is face up.
Homer And Ned's Hail Mary Pass - S16-E8
Continuity mistake: Homer is on The Front lawn when the bus of tourists turn up and Mario comes out. Homer gets mad and throws trash cans at Mario, who runs away and climbs up into the tree house which is at the side of the house, but it should be at the back.
Home Away From Homer - S16-E20
Continuity mistake: When Homer hits Coach with a chair, the white stripe that was on Coach's tracksuits has gone.
Treehouse of Horror XV - S16-E1
Continuity mistake: When Ned saves Moleman, we see where Ned is standing, there is no manhole beneath him yet when he catches Moleman there is one there. (00:02:30)
Continuity mistake: In the first shot of Selma on the hospital bed, there's nothing behind Patty. However, when Marge starts to speak, we suddenly see two bags of drip mounted on a dripstand behind her. (00:01:55)
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