The Great Race is a family of folk narratives explaining the order of the twelve animals: the Rat riding the Ox across the river and leaping ahead at the finish, the Rabbit crossing on logs, the Dragon stopping to bring rain, and so on down to the Pig. Versions vary by region and retelling.
The best-known episode is the Rat's. Unable to swim well, it rides across on the Ox and jumps clear at the bank to take first place — which is why the cycle opens with the smallest animal rather than the strongest. Most retellings use the sequence to explain something about each animal in turn: the Dragon arrives fifth despite being able to fly, having stopped to bring rain to a village; the Snake startles the Horse to take sixth place, with the Horse seventh; the Goat, Monkey and Rooster follow after working together; the Pig finishes last after stopping to eat and sleep.
A widespread variant explains an absence rather than a placing: the Cat is tricked by the Rat into missing the race entirely, which is offered as the origin of the enmity between them. In the Vietnamese zodiac, the Cat occupies the position held by the Rabbit in the Chinese sequence; that regional difference is separate from the Cat’s absence in this race story.
The race is a story told about an order that already existed. The sequence of the twelve branches is a calendrical structure considerably older than any surviving version of the legend, and the animals were attached to it rather than the other way round.