In the Warring States Period (zhàn guó 战国,475-221BC), a man in the State of
Chu (chǔ guǒ楚国) 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 enough wine for all them, and decided to each draw a picture of a 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 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.

战国时代有个楚国人祭他的祖先。仪式结束后，他拿出一壶酒赏给手下的几个人。大家商量说：“我们都来画蛇，谁先画好谁就喝这壶酒。”其中有一个人先画好
了。但他看到同伴还没有画完，就又给蛇添上了脚。这时，另一个人也画好了，夺过酒壶吧酒喝了，并且说：“蛇本来是没有脚的，你怎么能给它添上脚呢?”

“画蛇添足”这个成语比喻做了多余而不恰当的事，反而把事情弄糟了。

画蛇添足【翻译】Drawing a snake and Adding Feet.