Analysis: Sound Check
The speaker in this poem reminds us of one of those little red devils that sits on your shoulder and tries to convince you to do something bad. Maybe you haven't had the little-red-devil experience, but you've probably seen it on countless cartoons, as well as in a hilarious scene involving Tracy Jordan and Kenneth the Page on the TV show 30 Rock. Usually, there's a saintly angel to offset the devil, but there are no angels in this poem to advise the woman.
The devil speaks, as a good devil should, in simple and seductive rhymes...the better to charm your ears with! He thinks that if he turns his tricky arguments into songs, the woman will be less likely to think through their implications. Like the snake that tempts Eve in the Garden of Eden, the devil employs sibilance, or the repeated use of "s" sounds. In the first stanza, for example: "deniest," "suck'd," "first," "sucks," "know'st," "sin," "shame."
Also, he tries to make the woman feel guilty by adopting a theatrical tone, which comes through strongly when you read the poem aloud. It's almost as if the poem has stage directions: "alas" (he puts his hand to his forehead, sadly), "O stay" (he lunges to block her rising hand), "cruel and sudden" (he backs away from her, horrified).
Finally, he varies the rhythm, using lots of pauses (called caesuras) in the middle of the lines, which allows more time for the seeds of doubt and temptation to slip into the woman's mind. These pauses also help him turn the argument completely around in a heartbeat, as in the line: "'Tis true; then learn how false fears be." In short, he's a sneaky little devil.