Watch the Little Walter Approach online guitar lesson by Annie Raines from Blues Harmonica Blueprint
Here’s another way of blending octaves into the shuffle/march rhythm pattern. The octaves form a "call" that is answered and balanced out by the "response," single notes near the bottom of the harp. After each riff, the chord part provides a backdrop for the phrase to echo. This is a perfect example of using space to strengthen rhythm. You’re only playing one part at a time, but the repetitive timing "stacks up" in the listener’s memory, so you get two or three parts working at once.