Rhythmic Variation

In Poetic Closure: A Study of How Poems End, Barbara Herrnstein Smith describes how poems establish a pattern so the reader or listener can anticipate how the structure will continue. Imagine driving past a picket fence, and seeing the recurring pattern of one picket after another, evenly spaced. When the poem does something unexpected, like a break in that picket fence, it creates a sense of tension that gets relieved when the pattern is restored.

Music does this with tone as well as with rhythm, but it's a similar idea. A key or pattern is established, then set aside, and later restored. The relief of returning to the original structure helps create a sense of finality or ending.

At a finer level, this is done many times throughout some poems and musical works. The pattern itself may contain some variations in rhythm. Just think of that Bacardi Mojito ad that's all over TV these days. A simple, steady metronome beat would not be as effective in promoting alcohol consumption. (Well, maybe those models dancing have something to do with it, but if you close your eyes, it's still pretty catchy.)