Bob Dylan fans have spent the past few days online debating what song he opened with Saturday night in Chicago. The tune was first listed on Dylan's official website on Sunday as an instrumental rendition of "Rainy Day Women," but the respected Dylan fan site Bob Links called it "Sweet Home Chicago." Then Dylan's website later changed the title to "Instrumental Blues." Fans have been adding to the debate, saying the guitar parts sounds like Dylan's current arrangement of "Watching The River Flow" at times. No matter what the song is, it's yet another entry on the long list of Dylan mysteries. (Check out the first minute of the performance below.)