Kitten Kong - S2-E7
Revealing mistake: When the Goodies are at the park with their animals, Graeme tries to teach his tortoise tricks. When the tortoise jumps, you can see the wire making it 'jump'.
This Male Chauvinist Piggy Went to Market - S3-E1
Revealing mistake: When Laurie goes to flip Goose over her shoulder, it's obvious that a stuntman is actually flipped; he has much shorter hair than the actor portraying Goose. (00:11:45)
Revealing mistake: As Spring closes the door of the bus after looking for the spacemen outside the walls wobble.