The legend goes that either Buddha or the Jade Emperor called the animals together and there was a competition to see who could get across a stream first.  The rat asked the ox, who is good natured and ingenuous, if he could ride on his back.  When just about at shore, the rat jumped off the ox and claimed first place: the ox was second. 

Another part of the legend says that the cat was to be in the game, but one story says the mouse (rat) told him that it was the next day, and the cat missed it.  In another version of the story, the cat also ride on the back of the ox, but the mouse pushes him off.  That is why cats hate water and mice.

This year it is year of the ox.