Revealing mistake: When the dog picks up the stick of dynamite, you can see the stick is not lit, yet it still manages to blow up.
Continuity mistake: Throughout the race, watch the bands on the dogs. In some shots, they have numbers on them: others they don't.
Announcer: The dogs are going into their starting boxes. Now they're on edge for this race. Bill's Bunion looks a little sore. Pneumatic Tire's rounding into shape. Father's Moustache looks a little droopy. Motorman's Glove will have a hand in it. Bride's Biscuit is hard as a rock. Grandpa's Folly is out of it. He's being scratched.