Kumin has written a narrative poem that tells the story of killing the woodchucks in her garden, using an extended metaphor to compare this killing to warfare—and, at the end, to genocide. The poem shows how easy it can be to justify killing as righteous (the woodchucks deserve it) and how enjoyable it can be to eradicate the enemy when you have the preponderance of power.

The tone of the poem is light-hearted and tongue-in-cheek, which provides an antithesis to the seriousness of the subject matter. The banal is juxtaposed against the somber reality of woodchuck death: a "knock out bomb" comes from the local "Feed and Grain Exchange," showing a weapon of death placed casually alongside a store with a name that suggests nurturing (feeding), and in the next stanza, "cyanide" is juxtaposed to "cigarettes," another casually incongruous pairing of the lethal and the benign.

Kumin frequently uses assonance, which is when words beginning with the same vowel are placed in close proximity, and alliteration, which is when words beginning with the same consonant are placed near each other, in this poem. These literary devices add a sense of rhythm otherwise missing in this casually conversational, unrhymed verse and allow Kumin to place emphasis on certain words. Note the alliterative "s" sounds in:

shoehorned shut with puddingstone,
but they had a sub-sub-basement ...

and

state-store Scotch, all of us up to scratch

and the assonance in the "a" sounds in

the case we had against them was airtight

Killing weaves in casually with the daily life of shoehorns, stones, and basements, and the woodchucks have brought it on themselves for:

nipping the broccoli shoots, beheading the carrots.

Although the speaker clearly lives amid the abundance of American society, with many stores in which to shop, she uses the few nibbles on garden vegetables as justification for declaring war, implying that human survival is at stake: The woodchucks take:

The food from our mouths, I said, righteously thrilling
to the feel of the .22

The light-heartedness woven into to the narrative ends abruptly, however, in the last couplet, when the speaker compares killing woodchucks to the Nazi genocide against the Jews, suggesting that the one leads to the other:

If only they'd all consented to die unseen
gassed underground the quiet Nazi way.

Literally speaking, this poem is about someone attempting to kill the woodchucks that have become pests in a garden. On a deeper level, it is about the ease with which a man can become a killer during a war.

The end of the first stanza indicates that the woodchucks evaded death by retreating to a "sub-sub-basement" to escape the "knockout bomb" that had been prepared for them. This could be likened to trench warfare.

In the third stanza, the narrator provides justification for the onslaught of the attack, stating that the woodchucks are taking "the food from our mouths," implying that killing the woodchucks was a matter of survival, which is a common message of propaganda during wartime.

After the death of a couple more woodchucks, the narrator mentions how "the murderer inside me rose up hard," implying that the longer a war goes on, the easier killing becomes.

The last two lines of the poem provide a direct comparison between killing the woodchucks and the Nazi death camps, referring to gassing as an easy, impersonal way of killing someone.

Kumin's poem is an extended metaphor about how people are able, in their own minds, to justify violence against others.

The speaker begins by describing a relatively passive and discreet way of killing the woodchucks that are devouring her garden. She traps them underground and attempts to poison them. When that fails and the woodchucks eat her marigolds, broccoli, and carrots, her indignation deepens into what she believes is righteous anger, and she takes to shooting them with a .22 rifle.

Her justification for killing the animals is that they are stealing "the food from our mouths." One wonders if she really eats marigolds. She invokes Darwin's "survival of the fittest" and takes pleasure in killing, one after another, a whole family of woodchucks, marveling at how quickly she has warmed to becoming a sniper. She even adopts gunslinger descriptions like "I dropped the mother."

She recognizes her obsession with one woodchuck who evades her and wonders why he and the other woodchucks couldn't just die in the manner of the Nazis' victims: quietly poisoned, out of public view. It's as if she blames them for awakening her overt brutality--something she might prefer to keep under wraps.

The poem underscores how readily people's malevolence is awakened when they feel affronted. It is ironic that Darwin's name should be invoked, because the gardener's response is not a very "evolved" way of thinking. The speaker seems very self-aware yet unable to transcend a fairly barbaric reaction to another creature's attempt to survive.

This poem is about attempts to eradicate woodchucks from a garden on a literal level.  On a figurative level, it is about how little it takes to turn a person to evil.

In the poem, the speaker is trying to eliminate an infestation of woodchucks.  The speaker first attempts to take out the woodchucks in the most humane way possible by gassing them with cyanide.  When the “merciful” method does not work, the speaker gets more and more frustrated.  The woodchucks are still destroying the garden.

I, a lapsed pacifist fallen from grace

puffed with Darwinian pieties for killing

Soon she takes a shotgun and begins shooting the woodchucks.  The speaker justifies this by the fact that she is killing the woodchucks, but she is actually beginning to enjoy it.

The key to the poem is in the last lines.

If only they'd all consented to die unseen

gassed underground the quiet Nazi way.

Although all of the woodchucks are gone, they have left a lasting effect on the speaker.  The speaker cannot be the same person, and has instead been turned into a killer and one who enjoys killing, if only woodchucks.  The allusion to the Holocaust demonstrates that the speaker wishes to have been able to euphemistically avoid taking responsibility for the killing and acknowledging the result.