In the Warring States Period, a man in the state of Chu was offering a sacrifice（祭品） 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 decided¹ to each draw a picture of snake; the one who finished the picture 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（烧杯，大口杯） and drank the wine, saying,"A snake doesn't have feet. How can you add feet to a snake?"

This idiom refers to ruining a venture by doing unnecessary and surplus things.

故事：

楚国有一家人，祭过了祖宗之後，便将一壶祭祀时用的酒，留给办事人员喝。办事人员很多，仅仅一壶酒，到底给谁喝呢？有人提议让每人在地上画一条蛇，谁画得快画得好，就把这壶酒给他。大家都认为这办法很好。有一个人很快就把蛇画好了。这壶酒就归他所得。这时，他回头看别人，都没有画好，就得意扬扬地说："你们画得好慢呀ⅵ等我再画上几只脚吧ⅵ"正在他画蛇脚的时候，另一个人已经把蛇画好了。那人把酒壶夺了过去说："蛇是没有脚的，你怎麽画上了脚？"说罢，就喝起酒来。

画蛇添上脚：比喻增添多余的东西。