in the period of the northern and southern dynasties(420-589) there was an expert archer1（*手） named zhangsun sheng.
one day he went hunting together with a friend. suddenly they saw two vultures（秃鹰） fighting for a piece of meat high in the air. his friend handed him two arrows, and said, "can you shoot down both vultures?" zhangsun sheng effortlessly killed both vultures with only one arrow.
this idiom indicates achieving two things with one stroke2.
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