Despite Guan Yu inwardly cursing Zhang Fei for being thoughtless, he was acting out of concern for his brother. And when Lyu Bu aimed to kill Zhang Fei, Guan Yu would certainly not stand aside simply because his younger brother had misspoken. Moreover, in Guan Yu's eyes, Zhang Fei had not spoken wrongly at all.
As Guan Yu blocked Lyu Bu's attack with his sword, Claw Yellow Flying Lightning beneath him let out a mournful whinny. A normal prized steed would have surely been shaken to death by such a blow, but Lyu Bu, completely incensed by Zhang Fei's repeated verbal jabs of "Three-Family Slave," held nothing back in his strike. Guan Yu felt a violent vibration in his chest, fearing the disparity was even greater than it had been at their previous encounter at Hulao Pass!