Hi Charla, Michael, and Michael,
I agree with Michael's description of the mechanics. One small refinement I might add is that as you settle backwards into Play the Guitar, I think the right hand describes half of a vertical circle, pulling backwards, then downward, and then pushing slightly forward as you settle a little onto the front foot.
Talking about primary and secondary energies as Michael Coulon has done is important, because, as I understand it, all the energies are more or less present in all the postures and so you kind of have to figure out how they add up together. Another way to say this is that we have to think about what we are doing to our opponent's center, rather than to a particular arm or wrist.
Another thought I have about the contrast between Play the Guitar and White Crane Spreads Wings is that the shape of the left foot/leg and the right hand/arm seem to me to mirror each other somewhat. In White Crane, we are attempting to open up our opponent's center and the left leg and right hand/arm have convex, upwardly curved shapes. In Play the Guitar, we are trying to uproot our opponent's center by using his or her arm as a lever and our left arm as a fulcrum. Here the left foot/leg and right hand/arm have more concave, downwardly curving shapes.
Michael (mluddite), you talk about having the ball of the foot help the left hand to curve? I am not sure I feel that, can you elaborate on what you mean?
As I write this post, I wonder about Needle at Sea Bottom. Here is a posture with clear downward energy, but where the ball of the foot touches as the body sinks. Any thoughts?
As I perform the posture and ask myself why a heel touch feels inappropriate, I think of my hips. At the beginning of the posture, having my heel touching helps me open my hips, but as I sink, the fold at my waist becomes more important as the ball of the foot touches. Perhaps, a need for rotational energy at the hips implies using the heel, but the need for moving energy up and down the spine requires use of the ball of the foot.
Alternatively, perhaps the shape of the left foot/leg matches the shape of the downward curve of the sinking right hand or prepares for the subsequent rising energy of the body. Certainly having my heel touch as I sink makes me feel like I am pulling my opponent into my feet and under my center.
Perhaps, rather than speaking of having downward energy prominent, I should distinguish between downward "push/press" (an) energy in Play the Guitar and downward "pluck" energy in Needle at Sea Bottom. I think of push/press energy as compressing my opponent's energy flow downward and pluck energy as overextending it so that he or she topples over.