Revealing mistake: When Arran is pushing his gran at high speed in her wheelchair through the care home corridors, it is obvious that his gran is a dummy.
The Great Treasure Hunt - S2-E19
Revealing mistake: When Fester gives the anchor to Morticia, she drops it, and it bounces back up. When she lays it down, the wire used to achieve the gag is easily seen.
Revealing mistake: During the show when doughnut dressed as a tramp sits on the end of the bench and his weight causes tiger, who is sitting on the other end of the bench, to go up in the air, you can see the wires lifting her.
Revealing mistake: The "hostage" episode reuses footage from the "Dinosaur" episode, which doesn't totally fit. When the giant crabs attack and destroy the group of houses on the island, the longshot of the damage is recycled from the earthquake episode - including an earth fissure, something the giant crabs wouldn't and probably couldn't have done.
Aunt Bee's Cruise: Part 1 - S1-E15
Revealing mistake: Aunt Bee is traveling on a cruise ship. The "water" in the background is a painted backdrop which is made all the more obvious by the painted whitecaps.
Revealing mistake: During the opening theme, when the children are watching the magician, you can tell they were not actually filmed together. The magician scenes are filmed more professionally using a sharper tape or film image, whereas the children scenes look more like a standard fuzzier film-type such as on a projector (primarily used at that time).
Episode #1.5 - S1-E5
Revealing mistake: When the automated forklift picks up Harvey and places him on a shelf you can see the wires of the harness he is attached to coming from behind each of his shoulders. (00:15:28)
Revealing mistake: As Pat Buttram enters the office of the Bugle newspaper, he casts a shadow on the painted backdrop of the buildings across the street. (00:19:30)
Cruise (1) - S3-E6
Revealing mistake: In the beginning of the show, Shirley is ironing Laverne's clothes and leaves the room. The iron falls on Laverne's clothes on the "L" and burns it, When she picks up the iron, the "L" is on the bottom of the iron facing the normal way when, in fact, it should have been a reverse image.
Revealing mistake: A little oversight on the part of the producers. At the final scores that we are shown, Amy has $10,000, TJ has $9,800, and Travis has $2,400. This all adds up to $22,200. Even if they only answered $400 questions (which we can see that they don't), that's about 55 questions at best, only in the first half. That would run way longer, probably about three or four times as long, as any normal game show. And there's no mention of any other rules regarding the scores so there's no reason to think that there are bonus questions that could raise it that much.
Revealing mistake: When the house starts to shake and collapse the picture frames on the table don't move an inch, revealing that it's just the camera shaking.
Revealing mistake: When Cissy is at the piano as Buffy sings and dances for Uncle Bill, only her arms move up and down instead of across the keys, indicating that's it's an off-camera person actually playing the tune. (00:16:30)
Revealing mistake: Whenever Isis has to do jumps you can tell it's not her but a stunt double.
The Darkest Hour: Part Two - S4-E2
Revealing mistake: At the very beginning of the episode, as the knights are about to send Merlin to Camelot with Lancelot, the knights walk towards the camera. As they do, there's a patch of green screen the special effects department must have forgotten to remove between Sir Elyan and Sir Percival. (00:02:10)
Revealing mistake: Logan gets all the characters to spend spring break at his dad's house. When Zoey finds out Dustin drank all of Quinn's "fratz" she screams his name and runs to go and find him, but despite being meant to be angry you can tell she's laughing.
Revealing mistake: When Andi walks into the library (this is not Andi's dream) it cuts to the librarian sitting at her desk and we can see the shot is flipped - note the bookcase and the librarian's buttons. (00:10:40)
Revealing mistake: Angelica and the other children are about to crash through the door to attack Lyra and Will. As Lyra runs past a cabinet, a lamp sitting on top is knocked over and crashes to the floor. Dafne Keene, who plays Lyra, reached over and very obviously pushed the lamp to the floor.
Dawn and the Haunted House - S1-E2
Revealing mistake: Stacey can be heard whispering instructions to the kids she and Dawn are watching.