Before the poem says anything, its title does something strange. "Haustorial" is a botanist's word. A haustorium is the rootlike organ that a parasitic plant, mistletoe for instance, pushes into its host to draw out nourishment. It is an odd word to set above a walk in the woods, and it asks us to read everything below it as a story about living on, in, and through other things.
The first stanza gives us the host and the pests. We hear "porcupine teeth / in the oak's crown," and the sound is the only evidence we get. The porcupine is never seen. Then comes the simile "as lethal as mistletoe," which jars deliberately. Mistletoe usually means Christmas kisses and decoration, but here it is a slow killer, and the poem sets a gnawing mammal beside a clinging plant as if they were the same kind of threat. The sounds help the comparison along: the long *e* of "teeth" returns later in "three" and "deer," and the hard *t* and *k* sounds in "teeth," "crown," and "mistletoe" give the lines a gnawing, clicking texture.
The second stanza shifts from sound to sight, but again we see only traces. The deer are gone, and what remains is "the tracks of three deer / braiding and unbraiding." That last phrase is the poem's loveliest. The deer prints weave across each other like strands of hair or like a braided stream, and the paired verbs make the pattern both plait and loosen in front of us. After the one-way draining of the parasite, this is a picture of give and take, of lines that cross and part and cross again. The speaker is "ahead of me on the path" only by implication. He follows animals he cannot see, which makes him a reader of signs rather than a master of the scene.
Then the poem turns inward. "I reach inside my coat / and find a twig." The action is ordinary, and nothing suggests the speaker put the twig there deliberately. The line break after "It's happening" leaves the pronoun hanging for a moment before "sooner than I thought" arrives. The poem never says what "it" is, and that gap is where its meaning lives. Judging by the imagery, the likeliest reading is that the speaker is being drawn into the woods' own economy. The twig has found its way inside his clothing, as if the forest were already moving in. He may be the host here, slowly taken over by the place, or he may be a creature that belongs to it, like the porcupine and the deer. Either way, the phrase "sooner than I thought" carries a faint chill. It could point to winter, to ageing, or to the body's eventual return to wood and soil. The tone is so casual that the unease sneaks up on us.
The form supports that understatement. Three unrhymed tercets, short lines, no punctuation more dramatic than a full stop: the poem sounds like someone murmuring an observation on a cold walk. The stanzas also follow a quiet progression from the canopy ("the oak's crown"), to the ground (the tracks), to the speaker's own body (inside the coat). The poem moves steadily downward and inward, from tree to path to person.
It is also built almost entirely from evidence rather than presence. We get a sound, some tracks, and a twig, and not one of the creatures appears. That is a good way to write about a landscape where life is mostly known by what it leaves behind. It also suggests that the speaker himself is becoming a trace, something that will one day be found, like a twig in a pocket.
What makes the poem significant is how much it holds in twelve or so lines. It turns a scientific term into a way of seeing, replaces the pastoral idea of nature as scenery with something more intimate and more unsettling, and ends on a discovery too small to be dramatic and too odd to dismiss. The reader is left holding the twig, with the same quiet question the speaker has: what exactly is happening, and how soon?