Two Dozen and One Greyhounds - S6-E20
Continuity mistake: There are twenty-six puppies eating from their bowls in the kitchen. As the title suggests, there's meant to be twenty-five.
Two Dozen and One Greyhounds - S6-E20
Continuity mistake: When they are in Mr Burns' laundry room, it is shown that Bart wasn't wearing his socks. However, part way through this scene, Bart is wearing his shoes and socks again without having time to put them on.