The language Frost uses in his poems is always carefully chosen to convey the feeling or meaning he wants to create. Certainly, the words he uses to talk about the saw, from the very beginning of the poem, contribute to the impression of potential danger associated with the saw.
The poem repeats the phrase three times - "The buzz saw snarled and rattled in the yard...snarled and rattled, snarled and rattled." Calling the tool a buzz saw somehow seems more threatening than calling it a chain saw or a power saw. The word snarled immediately reinforces the feeling that this is not a friendly saw. To say that it rattled could remind the reader of other things that rattle, as in this foreshadowing of the rattling skeleton of death's approach.
When the snarling, rattling saw "leaped out at the boy's hand," the reader instinctively knows that this is a dangerous turn of events.