Mike Stone's poem is only three lines long, but it holds a whole season's ending. A single butterfly, the last one of autumn, appears, and the speaker seems stopped by it. Nothing else happens. There is no description of color or movement, just the sense that this small creature arrives and the world goes quiet around it.
The strongest image is "a chord of silence / strikes." Silence is usually an absence, yet here it behaves like music, a note sounded all at once. The odd phrasing suggests a feeling that lands suddenly and deeply. Judging by the words, that feeling is a mix of beauty and sadness: this butterfly is a final one, and its presence reminds us that warmth and life are running out.
The mood is hushed, tender, and a little melancholy. By breaking off on the single word "Strikes," the poem leaves us in that pause, as if we are standing still beside the speaker, watching.