Shallow the club by rotating the right elbow under
The move the coach calls the key of the lesson: shallowing the club with the trail (right) arm. From the top, where his right elbow points a bit outside his body, he rotates the elbow to be 'under' so it points straight down at the ground; this shallows the club with the arm and palm facing the sky. He identifies the result as the 'Hogan shallow position' at the top and calls it the most efficient position to deliver the club, letting it drop directly back to the ball with no urge to throw the hands, instead of coming over the top, getting steep, or flipping.
Channel: SagutoGolf
Watch official source at 7:29Why this context matters
Coach calls this the key piece ('golden nugget') of the lesson.