A long, long time ago, there were no zodiacs. Jade Emperor, the emperor of heaven, wanted a way to remember the years by representing them with animals. So, he invited all the animals to a race to determine who would get the spots.
Cat and Rat were good friends back then. When Cat heard the news, he asked Rat to wake him up when the race came. Rat agreed. On that fateful day, Rat got up on time. But he's a rat, after all, so he snuck off to the race on his own.
By riding on the back of the hardworking Ox and jumping off right at the finish line, Rat was able to get first place. The Ox finished second, followed by the fearsome Tiger. The Rabbit hopped into fourth. Dragon, who was caught up in some unfinished business, came in fifth. Slowly, more and more animals began crossing the finish line, but Cat was still cozying in bed.
By the time Cat woke up, it was all too late. The race was long over, with the Pig becoming the final zodiac. Cat was outraged. All the love between Cat and Rat shattered to pieces, turning into a burning hatred that lasted generations since. So, the next time you see a cat chasing a rat, you know why.