The poem opens with the speaker repeating a question that apparently has just been asked: what is the "most unusual thing" that the speaker ever stole? The speaker’s opening question is more specifically an instance of aporia: the speaker poses this question in order to answer it—to tell whoever the speaker is addressing about this "most unusual" theft.
The fact that a snowman is the “most unusual thing” the speaker stole implies that the speaker has stolen many other things as well. And a snowman is, indeed, a rather strange thing to steal. After all, a snowman has no material value; it's not something that the speaker could sell, and it seems like a tricky thing to move from one place to another. The snowman also evokes childhood, innocence, and joy. The fact that the speaker stole the snowman, then, alerts the reader to the speaker’s cynicism and lack of empathy.
The speaker took this snowman in the middle of the night, and describes it as looking “magnificent” while standing alone, “tall” and “white,” under the “winter moon.” The speaker personifies the snowman as “he” and also represents him as a “mute,” or a person who is unable to speak or communicate. This personification is important, since the poem will go on to suggest that the speaker identifies with the snowman and that the snowman—which is isolated, cold, and unable to communicate—is essentially a mirror of the speaker.
The poem is written in free verse, without a regular meter or rhyme scheme, and it feels casual and conversational as a result. At the same time, several sonic devices fill these lines with music.
For example, sibilant alliteration, as well as assonant long /oh/ sounds, link “stole” and “snowman,” while /m/ and /w/ sounds appear in “snowman,” “midnight,” “magnificent,” “mute,” “moon,” “white,” and “winter.” All these shared sounds might subtly evoke the speaker's fondness for the memory of the snowman theft.