"Spring" sounds like what it is: a song. But what gives "Spring" its song-y sound? We're glad you asked.
There are at least a bazillion pop songs out there (really, we did the math) and, while they are different in content and tune (sort of), they do all have something in common—they all have a chorus.
A chorus, or a refrain in poetry, is the lines that get repeated at least a couple of times throughout the song. You know what we're talking about, the part of a song you actually remember and can sing along to—that part.
Well, "Spring" definitely has a chorus. It's the five lines at the end of each stanza. So, the chorus helps make this feel like a song. But wait, there's more.
Take a look at the first four lines of each stanza. Notice anything? Yup, with the exception of one "do," all these lines begin with either "when" or "and." This repetition of initial words also adds to the song-like sound. Plus all those "when"s and "and"s make "Spring" sound like it's building up to something big—it builds tension. "And when," "and when," "and when"—feel it?
There is one other kind of repetition in "Spring." Take a look at the chorus's second line:
Mocks married men; for thus sings he
Hear those repeated Ms? That's what's known in the poetry world as alliteration. It has a way of making words sound like they belong together, and it makes for pretty catchy lines and phrases. This alliteration, coupled with those iambs we talked about in the "Form and Meter" section, make "Spring" a veritable toe-tapper.