This song would be considered "next-to" a cappella - it contains only one actual instrument, that being a bass guitar. Everything else is voice, snaps and claps.
The song is a tribute to the Doo-Wop sounds of the '50s that Joel loved, complete with lyrics about being crazy in love with a girl. The song began, however, as a classical piano piece Joel was working on, which is also how is song "Lullabye (Goodnight, My Angel)
" came about.