打草驚蛇

唐朝的時候，有一個名叫王魯的人，他在衙門做官的時候，常常接受賄賂、不遵守法規。有一天，有人遞了一張狀紙到衙門，控告王魯的部下違法、接受賄賂。王魯一看，狀紙上所寫的各種罪狀，和他自己平日的違法行為一模一樣。王魯一邊看著狀紙，一邊發著抖：「這...這不是在說我嗎？」

王魯愈看愈害怕，都忘狀紙要怎麼批，居然在狀紙上寫下了八個大字：「汝雖打草，吾已蛇驚。」意思就是說你這樣做，目的是為了打地上的草，但我就像是躲在草裡面的蛇一樣，可是被大大的嚇了一跳了！

後來，大家就根據王魯所寫的八個字「汝雖打草，吾已蛇驚」，引伸為「打草驚蛇」這句成語，用來形容對付別人的時候，因為一個無心的小動作，卻讓對方覺察到而提防警覺。

To Mow The Grass And Scare The Snake

Wang Lu was one of the magistrates of Dang-tu County during the T'ang dynasty. He was never concerned with how he could best serve the people; all he cared about was making money.

One day, the people of Dang-tu County got together and wrote up a complaint against Wang Lu's subordiante. They described very clearly how the subordinate had taken money that didn't belong to him, and then sumbitted the report to their magistrate, asking him to punish the subordinate.

When Wang Lu read what was written in the report, he began to shake, as he realized that he himself had done almost exact same illegal things. By the time he finished it, he was sweating all over, and paralyzed with fright in his chair. He didn't know what to do about this, and he couldn't help writing on the report, "Although your goal was to mow the grass, you wound up scaring the snake."

Thus, "To Mow the Grass and Scare the Snake" is to fail to keep one's actions secret, thereby allowing others to take precautions.