One day, the King of Heaven called all the animals to a meeting. He told them that he had decided to pick the 13 most pious animals and reward each of them with their own year.  The King set a contest. He told the 13 animals that it was The Buddha's birthday tomorrow, and that the first to congratulate the Buddha would have the honour of the first year, and the second to arrive would have the second, and in this way, the order of all the years would be decided.
That night the rat went to see his best friend the cat to discuss the race. They both agreed that the contest was unfair to them, as near the Buddha's house was a river, and both of them hated water, and neither were strong swimmers.
So the pair went to see the Ox who was very large and a strong swimmer. He was also extremely good natured, and he agreed to carry the rat and the cat on his back.
The next morning, most of the animals were up early. The Ox looked round for his friends, but he could not catch sight of the cat, or the rat. When he got to the bank of the river he was about to jump in with a great splash when the pair sprang out of the reeds and landed on his back. In this way, they set off into the deep, swirling waters of the river. Fortunately the Ox was powerful enough to swim across the current without any trouble, and soon the far bank was in sight. The cat crouched on the Ox’s head and swished his tail. The rat could see that his friend was getting ready to leap onto the bank ahead of them and take the first prize. He became so cross about this, that he pushed the cat into the water. Then he himself jumped onto the bank and won the honour of the first year for himself.
The Ox lumbered on, reached the house just after the rat, and the second year was named after him. The Tiger loved water, and he had powerful muscles and managed to come in third. He was followed by the rabbit - who was helped by the dragon.
The horse was about to come in sixth, but he reared back to avoid stepping on the snake who slithered in just ahead of him. So the snake was sixth and the horse was seventh.
Next came a raft with the sheep, monkey and the rooster who took the eighth, ninth and tenth places.
Quite a while later, the dog paddled ashore and shook himself so that he sprayed all the others who had just managed to get dry. The dog took the eleventh year.
Finally, after a long, long time, the pig made it to the bank. He had slept in late, and only just made it to become the 12th animal of the Chinese Zodiac.

And what became of the cat? He was swept downstream by the strong current of the river, and he very nearly drowned. Eventually, he was washed up onto the wrong bank, the one where they had all started, and he shivered and shook with rage, and did not meet the Buddha. And so there are 12, not 13 years in the Chinese calendar, and there is no year named after the cat. And if you’ve ever wondered why cats hate rats so much - now you know !