Zhang Su, Zhang Song's brother, discovered his brother's secret communications with Liu Bei and reported the issue to Liu Zhang. Liu Zhang was furious and stunned when he heard that Zhang Song had been helping Liu Bei to take over Yi Province from him – he executed Zhang Song and ordered his officers guarding the passes to Chengdu to keep secret his knowledge that Liu Bei wanted to attack him. Nevertheless, Liu Bei still found out from the spies he planted around Liu Zhang. Fa Zheng and Meng Da defected to Liu Bei's side before Yang Huai (楊懷) and Gao Pei (高沛), Liu Zhang's subordinates guarding Boshui Pass, knew about Liu Bei's true motive. Liu Bei lured Yang Huai and Gao Pei into a trap and executed them for behaving disrespectfully towards him. He then took command of Yang Huai's and Gao Pei's troops, numbering under 5,000, and turned to attack Fu County (涪縣; present-day Mianyang, Sichuan).