In 756, during the An Shi Rebellion, the Tang emperor Xuanzong's favorite concubine Yang Yuhuan (Yang Gui Fei) was done to death below Mawei Hill, and Xuanzong fled into Sichuan. The rebel armies were far away, but at dusk under a sullen, overcast sky, the sound of the cuckoo's song of blood redoubled the heartbroken emperor's grief.
安史之亂，馬嵬坡下，楊玉環被難斷送了性命，唐明皇匆匆奔逃蜀中，賊兵雖遠，但陰雲黯淡天昏瞑，哀猿斷腸，子規叫血，讓個唐明皇脫口說道「好教人怕聽！」