During the Warring States Period, a man in the State of Chu held a sacrifice to honor his ancestors. After the ceremony, he gave a beaker of wine to his servants. The servants, thinking the wine insufficient for all, decided to hold a contest: whoever finished drawing a snake first would win the wine. One servant finished his drawing very quickly. Seeing the others still busy, he confidently added feet to his snake. At that moment, another man finished, snatched the beaker, and drank the wine, declaring, "A snake has no feet. How can you add feet to a snake?"
This idiom means to spoil something by adding unnecessary and superfluous details.