When you cannot detect the opponent's plans launch a direct, but brief, attack and observe your opponent reactions. His behavior will reveal his strategy.

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During the Tang dynasty, there lived a corrupt county magistrate named Wang Lu. The people made an indirect attack on him by accusing his bookkeeper of embezzlement. Without thinking Wang wrote, "By merely beating the grass, you have startled the snake within".

In the year 627 BC, Qin general Meng Mingshi led his forces to attack the state of Zheng bordered by Jin. Before he set off, Qin's top advisor Qian Shu cautioned him, "Beware of enemy ambushes when you pass Mount Xiao in Jin."

The Qin troops arrived at Mount Xiao. He was about to order his troops to advance when his two assistant generals Xi Qi and Bai Yi warned him: "We are attacking Zheng after Hua. The overlord of state of Jin won't like this. Now that we are at Mount Xiao we should be careful." "Mount Xiao is a dangerous place. We should search out its paths to make sure it's safe."

Meng Mingshi did not think it was neccessary to take precautions. Upon seeing some Jin's troops, Meng Mingshi ordered his troops to charge to finish them off. The Jin troops disappeared and the mountain path was sealed off.

Meng Mingshi ordered the Jin flag to be brought down. As the flag fell, war cries broke out. Qin's troops were encircled by the Jin forces and slaughtered.