When serving as prime minister to King Hui of Qin, Zhang Yi developed a carbuncle on his back.
He summoned the renowned physician Sheng Gou to treat it, saying, "Consider my back as your own. Proceed with whatever treatment you deem appropriate."
Sheng Gou, a skilled doctor who had previously cured King Xuan's ailment, felt relieved of all pressure upon hearing Zhang Yi's words. He confidently selected the most suitable treatment based on his experience and successfully cured Zhang Yi as expected.