This is a study of the riff often called the “Box Shuffle” by guitar and bass players. It can be played ascending, or like this version, descending. The advantage of this is that it is highly recognizable to any band that is familiar with blues. This allows you to start the song off and signal the band in at the IV chord if your rhythm and playing are strong. This “Box” riff avoids the “3rd” of the chord, and is another way to look at playing the blues scale. This song does not have a turnaround on bar 12, which is common with this riff. I advise to work on the study song “Chicago Box Shuffle” before this.