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: When we see "Grandpa's Folly" being 'scratched' in his starting box, the box has no door in front of it, but when we see the boxes at the start of the race in the next shot, a door has suddenly appeared.
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.