During the Spring and Autumn period, the state of Qin sent three generals—Meng Mingshi, Xiqishu, and Bai Yibing—to launch a surprise attack on the state of Zheng. As the Qin army passed through the territory of Hua, a neighboring state of Zheng, they were spotted by Xian Gao, a Zheng merchant on his way to trade in Luoyang, the Zhou capital. Suspecting the army's true intent, Xian Gao quickly produced four cowhides and twelve oxen, pretending to be an envoy sent by the Duke of Zheng. He addressed the generals, saying, "Our Duke, hearing of your passage, has sent me to offer you these provisions." While stalling the Qin forces, he secretly dispatched a messenger to warn his homeland.
Upon receiving the report, Duke Mu of Zheng immediately thought of the Qin troops stationed within his state, fearing they might coordinate an attack from inside. These Qin soldiers had been left in Zheng two years earlier, when Qin and Jin had jointly besieged Zheng. At that time, Zheng sent Zhu Zhiwu to persuade the Qin army to withdraw, and under that pretext, the Qin forces left this contingent behind.
Duke Mu of Zheng sent his minister Huang Wuzhi to issue an eviction order to the garrison, saying, "You have stayed too long in our state; our grain and livestock are exhausted from feeding you, and we have no more provisions to offer. You must leave now—or we will not be polite!" The garrison commander, Qizi, and his officers, realizing they could no longer hold their ground in Zheng, withdrew their troops.
Upon learning this, Meng Mingshi told his officers, "The fact that Zheng has expelled Qizi and his men at this moment shows they already know our military objective and are prepared. A surprise attack is no longer possible. If we try to storm the city, it will be difficult to take; if we lay siege, we have no reinforcements. We should return home." So the Qin army conquered the state of Hua on the way back and withdrew to Qin.
Later, the idiom "Repelling the Enemy with Cattle Feed" came to describe using wisdom and strategy to drive back an enemy.
Source: *Zuo Zhuan*, Chapter "Duke Xi's 33rd Year"
Meaning of the Idiom: Later, the Chinese idiom "牛饩退敌" came to describe using wisdom and strategy to drive back an enemy.