Metaphor is a comparison of two different things. When you compare something to a human, that is a type of metaphor called personification. Poets use metaphor to evoke a mental image. In this moving poem about a farmer losing a hand, it is the stark language and disturbing images that add to the reader’s reaction.
The buzz saw is described as having “snarled and rattled” (line 1). A saw can rattle, but it can’t actually snarl.
The saw is then described in the same way a human would be.
At the word, the saw,
As if it meant to prove saws know what supper meant,
Leaped out at the boy's hand, or seemed to leap -
He must have given the hand. (14-16)
The saw cannot leap, and the saw is personified as thinking about supper. The poem ends as the boy dies.
And they, since they
Were not the one dead, turned to their affairs. (29-30)
The contrast between the imagery and the harsh reality is quite effective and disturbing.