Kamp Krusty - S4-E1
Continuity mistake: At the breakfast table, Homers plate of food changes entirely between shots. (00:02:50)
Kamp Krusty - S4-E1
Continuity mistake: When Lisa gets her report card, the big blue "report card" disappears from the card after she puts it down. (00:04:10)
Kamp Krusty - S4-E1
Continuity mistake: When Lisa is reading her report card, the writing suddenly appears on the back of the paper, even though she didn't flip the card. (00:04:10)
Kamp Krusty - S4-E1
Continuity mistake: Bart holds up his maths book but in the next shot the book is on the desk. (00:05:00)
Kamp Krusty - S4-E1
Continuity mistake: In the shot where Kearney is reading the letter sent by Marge whilst he is eating the jellybean cookies, there is a quick shot of Kearney's hand going to his mouth with the cookie to eat it. Note that there is nothing on his wrist. In the next shot where it is revealed that Kearney is reading the letter rather than Bart or Lisa, he has spiky, black collars on his wrist. (00:14:25)
Kamp Krusty - S4-E1
Continuity mistake: Homer points out to Marge that now that the kids are away, he has grown two more hairs, making it four on the top of his head. Later when they are reading Lisa's letter, he has two hairs again. But later still when they are watching TV, he has four again. Two of them fall out when he see that Bart is the ringleader, leaving him with his original two. (00:15:35)
Kamp Krusty - S4-E1
Continuity mistake: When the kids rip Krusty's shirt to see if it is the real him he buttons his shirt up then in the next shot his shirt is still torn.
A Streetcar Named Marge - S4-E2
Continuity mistake: As Marge is about to leave for her first audition, she walks across the room and she is wearing white slip-on shoes. Then her and Homer talk for a bit, then when it cuts to a wider shot after they talk, she now has her red flat-heels on. (00:03:30 - 00:04:00)
A Streetcar Named Marge - S4-E2
Continuity mistake: Just as Marge heads out for her 1st audition, the kids go from lying on the sofa to sat up instantly. (00:03:35)
A Streetcar Named Marge - S4-E2
Continuity mistake: When Marge walks across the living room she has a bag in her hand which disappears when the camera changes. (00:03:35)
A Streetcar Named Marge - S4-E2
Continuity mistake: Otto's tattoo changes from the close up and the long shot of him when auditioning for Stanley. Note the eyeballs. In the first shot they are past the top hat. In the following they are much further back. (00:05:30)
A Streetcar Named Marge - S4-E2
Continuity mistake: When Homer picks up the snacks from the vending machine, 2 items are left on the floor. When Marge is practising her lines a few shots later, the items have disappeared. (00:11:10)
A Streetcar Named Marge - S4-E2
Continuity mistake: When Maggie is looking down at the desk to see the keys, there is a book on the desk as well. When she's looking down at the adult walking into the room the book has gone. (00:14:00)
A Streetcar Named Marge - S4-E2
Continuity mistake: When Maggie fires the dart onto the locker, it's position in relation to the vent slits changes between the long and close up shots. (00:14:30)
Continuity mistake: When Homer spots the penny, he moves his foot and there is nothing on the floor. When the shot changes, the penny has appeared. (00:06:50)
Continuity mistake: Homer asks the family how church was. When he does, Marge grabs her nose. Camera cuts and she is no longer holding her nose. (00:07:30)
Continuity mistake: When talking to the family about no longer attending church, Bart moves behind Homer in an instant cut. (00:07:45)
Continuity mistake: Homer says he's had the best day by not going to church. When he does, Marge has Maggie in her arms. When the camera changes to behind, you can see she no longer is holding Maggie. (00:07:45)
Continuity mistake: Homer says he wasn't sure if he was doing the right thing in regards to giving up doing to church. When he does he puts his fork down across his knife. When the camera cuts the two utensils are no longer crossed. (00:10:40)
Continuity mistake: While Homer is sleeping, the fire burns off the hair on his head. But when he wakes up and jumps up off the couch, his hair is back again. (00:17:00)
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