Lisa's Pony - S3-E8
Audio problem: When Homer is crying after the tape is finished, what he says doesn't match his mouth. (00:07:25)
Lisa's Pony - S3-E8
Continuity mistake: After Homer watches the tape, Marge suddenly appears beside him. (00:07:30)
Lisa's Pony - S3-E8
Continuity mistake: In the last shot of Marge and Homer's discussion of buying a pony, we can see a door on the right side of the screen. This door changes position when Lisa rides in the bedroom with her pony. (00:08:45 - 00:12:10)
Lisa's Pony - S3-E8
Continuity mistake: When trying to get a loan, Homer is tapping his fingers on the counter. When the shot changes, his hands are by his side. (00:10:00)
Lisa's Pony - S3-E8
Continuity mistake: When applying for the loan, a bell appears on the counter in front of Homer. (00:10:00)
Lisa's Pony - S3-E8
Continuity mistake: In the kitchen, there is a clock on the wall that changes time from 07:10 to 09:10. (00:12:10)
Lisa's Pony - S3-E8
Continuity mistake: Before Lisa licks the salt lick, there is another horse in the stable which disappears. (00:14:30)
Lisa's Pony - S3-E8
Continuity mistake: When Ralph is sat on the fence watching Lisa, his position changes between shots. Note the fence post in relation to his body. (00:15:20)
Lisa's Pony - S3-E8
Audio problem: When Lisa rides past on her pony, Ralph is sitting on the fence with another boy who says, 'She really tamed that horse', Ralph says, 'Yes but who can tame her?' However he speaks with a deeper voice as opposed to his higher squeaky voice, and sounds exactly like Nelson Muntz. (00:15:55)
Lisa's Pony - S3-E8
Continuity mistake: When Lisa calls Homer at work, Homer picks up the phone on his left side. Instantly after, we see him hang the phone up on his right side. (00:19:00)
Lisa's Pony - S3-E8
Continuity mistake: When Homer is phoned by Lisa, the color of the phone is blue. Immediately after, it turns to green. (00:19:00)
Lisa's Pony - S3-E8
Continuity mistake: At the end, the melted cheese and work outfit disappears from Apu's hands. (00:21:20)
Lisa's Pony - S3-E8
Continuity mistake: At the very end, the outside of the Kwik-E-Mart is different. (00:21:35)
Lisa's Pony - S3-E8
Continuity mistake: When Homer tells the family where the horse will be kept, if you look in the background there are drapes on the wall. These drapes weren't visible when Marge and Homer walked in the kitchen.
Lisa's Pony - S3-E8
Continuity mistake: When Lisa calls Homer at work, you can see some monitors to his right, and a fire hydrant in back of him. When he turns to his right, you can see that the monitors disappear, the fire hydrant moves, and a green telephone appears next to it.
Lisa's Pony - S3-E8
Continuity mistake: At one point in the episode, Homer is on the phone with someone in his work station. I forget who it was, but anyway, when you first see him, the wire is coming from the left side of him and when he turns to his right, the wire is coming from the right side of him.
Lisa's Pony - S3-E8
Other mistake: When Lisa rings Homer to tell him that she loves him, the shot of her talking is re-used from "Bart's Dog Gets an F." We can tell this because her cheeks inexplicably appear puffed up (in "Bart's Dog Gets an F" she had mumps).
Lisa's Pony - S3-E8
Revealing mistake: At the end, Homer and Lisa don't cast a reflection on the Kwik-E-Mart's doors. They should, since they are only a few metres from it.
Continuity mistake: When McBane's partner asks him to do just one thing for him, the picture keeps appearing and disappearing from his hands. (00:05:30)
Continuity mistake: In the video store, when Homer looks at sports tapes, the categories of movies behind him change from drama, horror, and 'Elvis' to drama, western and horror. (00:05:55)
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