Picture a pilot letting go of the controls in mid-air. Nobody is steering, and yet the plane keeps its height and keeps heading the right way. That single picture — something carrying on correctly while no one is paying attention to it — runs through both uses of the word. Bolted into a plane it is a machine; borrowed for a person it is the state of hands that keep working after the mind has wandered off.
可以想成這樣一張圖：駕駛員在半空中把手從操縱桿上放開。沒有人在控制，飛機卻還是穩穩地保持高度、朝著對的方向走。這個「有人放手、事情照樣自己進行」的畫面，兩個用法都用得上。裝在飛機上，它是一台實際的機器；搬到人身上，它變成一種狀態——手還在動，心思已經跑掉了。