如ㄖㄨˊrú臂ㄅㄧˋbì使ㄕˇshǐ指ㄓˇzhǐ

像胳臂指使手指。語本《漢書·卷四八·賈誼傳》：「令海內之勢如身之使臂，臂之使指，莫不制從。」比喻指揮如意，得心應手。唐·獨孤及〈故江陵尹兼御史大夫呂諲謚議〉：「且訓其三軍，如臂使指。」反鞭長莫及

英as the arm moves the finger (idiom), freely and effortlessly, to have perfect command of