A walker comes across a rabbit trapped inside a ring of fencing, where it has squeezed in to nibble dogwood sprouts and now can't find the way out. The scene is small and quiet, set in crunching snow, but it turns tense the moment the speaker appears. He "looms up," a phrase that makes him sound huge and threatening from the rabbit's point of view, even though he may mean no harm.
What stands out is how the poem lets us see the speaker seeing himself. He doesn't say he feels guilty or sorry, but the word "loom" suggests he realizes what he looks like to a frightened animal. The final image, the rabbit beating against its cage "like a panicked heart," pulls us right into its fear. The creature becomes almost nothing but a heartbeat. The mood is hushed, tender, and uneasy: a moment of helplessness, and the discomfort of being the cause of someone else's terror.