The speaker talks directly to a porcupine that has stripped the bark from a pine, killing it. Instead of scolding, he asks odd, curious questions. Does winter bark taste different on a tree you've just killed? Does the animal, with its poor eyesight, prefer dark hollows and the undersides of things? The dead pine's pale branches glow like candles, a strangely beautiful result of the damage.
The tone is half-teasing, half-admiring. The speaker jokes that the pine was "unwise" to have such soft, tempting spines, and compares its hiss to a gnawed road-salted tire. That detail points to the porcupine's known craving for salt, which the final question picks up. Looking at the "bleached roads in the air," meaning the bare white branches, does the porcupine long for salt? The mood is quiet, wry, and a little wistful. The speaker seems fascinated by the animal's slow, relentless appetite, and he sees both ruin and beauty in what it leaves behind.