How would you describe Frost's tone in the poem "Out, Out"?

And then—the watcher at his pulse took fright.
No one believed. They listened at his heart.
Little—less—nothing!—and that ended it. 
No more to build on there. And they, since they
Were not the one dead, turned to their affairs.

How does Frost create a sense of horror in "Out, Out—"?

Frost uses a detached and emotionless tone to create a sense of horror in this poem. The closest that the narrator gets to expressing emotion is when he comments that he wishes "they might have said" to "Call it a day" and given the boy a half an hour off (in order that he might have avoided the accident completely). His description of the, frankly, horrifying accident is so devoid of extremes that we can almost misunderstand what happens. It is presented, somewhat ironically, in a completely unhorrifying manner. The narrator says,

At the word [supper], the saw,
As if to prove saws knew what supper meant,
Leaped out at the boy's hand, or seemed to leap--
He must have given the hand. However it was,
Neither refused the meeting.

He describes the saw cutting off the boy's hand (or nearly so) as a kind of meeting between well-intentioned, polite strangers, rather than as the completely blood-soaked horror show that it must have been. He employs a kind of understatement with this description, personifying both the saw and the hand as willing acquaintances.

The description of the boy's attempt to "keep / The life from spilling" is another strangely calm and almost poetic way to describe what happened. It employs metonymy as well, associating the blood that spills from his wound with the boy's life, as we certainly need our blood to live. Presumably his extreme loss of blood is why he dies in the end. This metonymy removes anything graphic from the description and makes it sound almost lyrical or beautiful.

In the end, then, the juxtaposition of the author's detached tone and the narrator's calm descriptions with the bloody and violent reality create a kind of horror. Why isn't the author or the narrator, or even the other people in the poem more upset?! The reason gets at the poem's theme: death is commonplace -- even when it happens so tragically and suddenly to one so young -- and life must go on. There is, honestly, something horrible about this idea too: that the extinguishing of life is so common that it ceases to produce any real effect.

How does Frost portray the saw as sinister in "Out, Out—"?

Frost's narrator says that the "buzz saw snarled," using a metaphor (implied by the verb snarled) to compare the saw to an angry and unpredictable animal. A metaphor compares two unalike things, claiming that one is another without using the words like or as. Animals, like dogs or cats, tend to snarl when they are very upset, and this high level of emotion (with limited means of expression) often result in some kind of violence—like biting, an action that draws blood and harms the one bitten (like the saw does when it cuts the boy). Later, the narrator says that

At the word [supper], the saw,
As if to prove it knew what supper meant,
Leaped out at the boy's hand, or seemed to leap—

Here, the narrator personifies the saw, giving it the ability to "know" what a word means and to "leap," or seem to leap. Personification is the attribution of human qualities to something nonhuman. By giving the saw life—either as an angry animal or a person with intention and understanding—Frost gives it a sinister quality. Anything that seems unpredictable, knowing, and dangerous would be.

Frost uses several techniques to ensure that the saw appears sinister and threatening in "'Out, Out--.'" First, "snarled and rattled," the sounds made by the saw, are repeated; they suggest a dangerous animal with "snarled" as well as the mechanical nature of the saw with "rattled." Will the beast attack? Is the saw somehow loose? The saw, furthermore, is given life with the verse, "as if to show saws knew what supper meant, /Leaped out at the hand, or seemed to leap--." Here the saw is depicted as a hungry creature that seems to attack the boy's hand, viewing it as supper.

The dangerous image of the saw is also suggested in the beginning of the poem with Frost's description of the setting: "from there those that lifted eyes could count / Five mountain ranges one behind the other/ Under the sunset far into Vermont." The scene foreshadows two images: first, the five mountain ranges suggest five fingers, red under the sunset--a bloody hand. Second, the sharp teeth of the saw are similarly suggested by the mountaintops glowing red under the sunset.