Question

Which line in the excerpt from “Out, Out—” by Robert Frost uses metonymy?
The boy's first outcry was a rueful laugh,
As he swung toward them holding up the hand
Half in appeal, but half as if to keep
The life from spilling. Then the boy saw all—
Since he was old enough to know, big boy
Doing a man's work, though a child at heart—
He saw all spoiled. 'Don't let him cut my hand off
The doctor, when he comes. Don't let him, sister!