Porter's first Broadway hit song was "Let's Do It," an endless catalogue of zoological promiscuity (some critics called it a "habits of rabbits" song) that captured the "just say yes" spirit of the twenties. Its musical sophistication matched its verbal aplomb. Porter had immediately broken some of the basic rules of American popular-song writing. Though you hardly notice it, the melody, beginning with its hook, is highly chromatic, and the harmony constantly mixes the major and minor modes in a way surprisingly reminiscent of Schumann or Brahms. It sounds like a simple tune—but try finding the notes and chords on the piano.