For a song to be catchy, it doesn't necessarily need to be enjoyable. If you've ever lay awake at night with It's A Small World or Macarena keeping you up, you understand the paradox. In fact, part of what makes a song catchy is purely biological, as we learn from one piece in Biorhythm: Music and the Body, showing through August 6 at Eyebeam Art And Technology Center in New York City.