Factual error: In "The Bully Proof Vest" Gromit is punched through a door, leaving a perfect shape of him as a hole in the wood, including both ears. Gromit is wearing a hat which keeps his ears hidden both before and after the punch.
Continuity mistake: In the episode 'The 525 CrackerVac' the vacuum cleaner malfunctions (as usual) and Gromit challenges the device like in a duel. The scenery changes to orange like in a sunset and Gromit stands with his back towards the window. On the window sill you can see a cactus. Wallace is in the room near the door. The vacuum cleaner explodes and covers Wallace in ashes/dust. Wallace suddenly has the cactus on his head (also covered in ashes) and judging by the fact that there is a clean area behind Wallace on the wallpaper in the shape of Wallace with a cactus on his head he must have had the cactus on his head before the explosion, but we know he hadn't as the cactus was standing behind Gromit and Gromit stays clean after the explosion, so the cactus couldn't have moved. How did the cactus end up on Wallace's head?
Continuity mistake: When Gromit gets punched in the face on "The Bully Proof Vest" short, his black eye is on the opposite side of which he got punched.