During the Warring States period, Zhang Chou, a minister from the State of Qi, was held hostage in the State of Yan. The King of Yan intended to kill him.

Zhang Chou seized an opportunity to escape but was caught by a guard at the border of Yan.

Zhang Chou, thinking quickly, told the guard that the King of Yan wanted to kill him because he possessed a precious pearl that the King coveted. He warned the guard that if he didn't let him go, he should claim that the guard had swallowed the pearl, and the King would then disembowel the guard to retrieve it.

Frightened, the guard had no choice but to let him go.