Frost doesn't just rely on boring old meter and rhymes to make music in this one. He's got alliteration, assonance, consonance, and slant rhymes up the wazoo to add some flavor to the mix.
We'll walk you through a few examples:
All these little sonic moments make this poem an echo chamber of sorts, with repetition in more than just its imagery. We're constantly being reminded of the poem's meaning with these clever repetitions, and they only enhance the fleetingness of the poem, as the silence when we're done is all the more deafening for it's lack of music.