In the Warring States Period, a man in the state of Chu was offering a sacrifice to his ancestors. After the ceremony, the man gave a beaker of wine to his servants. The servants thought that there was not enought wine for all of them, and decided to each draw a piecture of snake; the one who finished the piecture first would get the wine. One of them drew very rapidly. Seeing that the others were still busy drawing, he added feet to the snake. At this moment, another man finished, snatched the beaker and drank the wine, saying,"A snake doesnt have feet. How can you add feet to a snake?"
This idiom refers to ruining a venture by doing unnecessary and surplus things.