The vocals in this song follow one melody in the foreground, while the instruments are in the background (this is only false for a small portion of the song when there are no vocals). To keep the vocals interesting, the two vocalists switch back and forth. There is more activity in the vocals than in the instrumentation, so it attracts the attention (action). On a related note, since the background music is sort of generic, the vocals attract the listener even more because it's more original (novelty). After keeping the song pretty repetitive, at 3:25 the entire song takes a huge turn(which changes the momentum), bringing the attention of the listener back to the song. This song is lighthearted and fun, and could easily be the theme song to a sitcom.
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