More Consistent Shakes - Part 2 (Arcing off the Harmonica)
Now that you've practiced having your nose centered between the two holes you're performing the shake on, we can use this as a tool to get better at doing shakes across the range of the harmonica. Let's first focus on general movement on the harmonica.
Go in front of your mirror again and play a 4 draw. If you turn your head to the right (nose at 1 O'clock) you'll play a 5 draw. If you keep turning your head to the right (2 O'clock), your lips start to arc off the harmonica, but you may still be able to play a 6 draw, though there there will be some air leakage. Turning one more click of the clock to 3 O'Clock you're now completely off the harmonica.
Observing this, we can make a general rule. You can turn your head one hole to the left or the right without any issues, but when moving more than one hole, move the harmonica. You can move your head side-to-side, parallel to the harmonica, but it too his its limits of range and is generally discouraged due to your head no longer being over the center-line of your body... your neck muscles are no longer working in a balanced way.
Now play a shake again, focusing on centering between the two holes you're performing the shake on. Feel that when turning your head to the left that the left neck muscle is slightly flexing and the right relaxing... then the stored elastic energy of the right muscle that is now being stretched returns your head to center and then slightly flexes to bring your head to the right-most hole. The shaking motion should be centered, relaxed and smooth... no tension involved.
Experiment with this some more and we'll start moving across the range of the harmonica tomorrow.