This song is great for the representation of freedom that old time music is. It has been done dozens of different ways by dozens of different artists. The words change, but the chord progression and melody are basically the same and became the foundation for "Liza Jane", "Pig in a pen" and others. I've seen it titled as "Whoa Mule", "Ol Gray Mule" and my favorite, "Johnsons Old Grey Mule ". (www.youtube.com/watch?v=U24XpGGFIgA) This one is particularly entertaining!(and explains the wahl wahl wahl!) Also check out this...(www.youtube.com/watch?v=5qIGOd_W5gg) The Dillards did this on a Mayberry episode with Andy Griffith as well.