Ups 'n Downs (1931) - Public Domain Cartoons

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Summary
Bosko, working as a hot dog salesman at a fair, is determined to win the fair's race with his self-built mechanical horse. Despite fierce competition from riders and their legislate horses, along with the efforts of a cheating jockey who uses his spit and even a hand grenade to hinder Bosko, Bosko crosses the finish line using his horse's extendable neck and is crowned the winner of the race.

Alternate version and ending
When the cartoon was re-released by pirate distributor Astra TV in the 1950s, it was renamed Off to the Races and had a cut ending.[3] In the redrawn colorized version, the hand grenade destroys Bosko's mechanical horse, but also sends him flying into the cheating jockey and knocks him off his own horse, which Bosko is then able to use to win the race.