This move was mentioned earlier in the discussion of using edges as wings to engage the current. Hopefully you have practiced this enough to feel comfortable entering an eddyline, lining up your angle of attack, and sinking into the current. For the mush move, we are going to add on to that. As your bow sinks into the current, reach your paddle into the current (right edge, right paddle blade), and pull your stern edge down to where your bow has sunk. After a little practice, you should be able to get your entire head underwater in most decent eddylines.