LC:
My practice of Chan-ssu ching is an actual physical technique involving the use of visualization, and waist movement to generate circling, and spiralling movements throughout the body. It is very easy to grasp even though it involves a heightened awareness of one's own body, and how it is anatomically connected. It is simply linking the entire body while moving slowly at first, and eventually (after a great deal of careful study) very fast. This is what makes it so dangerous for the player (as well as the partner or opponent). The technique is very hard to control at first, but there is nothing mysterious or supernatural about it. It is a very powerful physical technique and I believe it to be the main one that makes the art of Tai Chi so devastating as a martial art.

TC:
OK, that goes with what I've gathered so far, depending on the nature of the visualizations. The references I've found call for flowing, say, a hand around a path following the tai chi symbol, with the (say) hand movements guided by the shoulder, waist, etc. and working towards the the nature of movement described in the classics. I've found standing, moving, hand and foot practices, and can probably extrapolate to the body at large as my kinesthetic awareness improves. I don't have any specific visualizations beyond the path itself, though; I simply work on the mind leading the chi leading the movement from the tan tien. There are also a fair number of "coiling" and "spiraling" exercises not lumped under the chan-ssu chin title, with more internal visualizations (meditations) that would seem to relate, but I'm not yet sold on their validity (those specific exercises I've found, I mean).

LC:
Your description is pretty close to the point. As far as visualizations go I simply "get inside" the movements. That is, I find I am able to be quite subjective while maintaining an "objective" external awareness simultaneously. This is a trick I believe I learned as a road musician - believe it or not. You are probably aware that when one is playing any musical instrument (mine happens to be keyboards), that at some point there is a secondary awareness that kicks in and one can play/perform with almost two distinct consciousnesses running side by side. I am also a professional magician, which requires the same kind of dual awareness. (Performing a set of practiced movements while "standing in front of myself" and presenting the results in a theatrical manner!) I find this to be about as close to a meditative state as anything else I've ever tried or heard/read about. I believe it is very close to the kind of head space that people who claim to "channel" are in... but of course with chan-ssu chin I am not pretending to be Lazarus or some alien god from the fevered planet of the mind. So visualizations for me and my students are kept pretty much to "picturing what is moving in what part of the body, and where is the kinetic energy going/coming to/from! and ".. picture how you could use it". You can use it for anything from opening a pickle jar or taking the stiffness out of your shoulders and back to bringing your training partner to meet the floor either gently - or with no dignity.

TC:
I understood a goal of shrinking the scale of the movements toward incorporating them into the form and applications with little outward visible evidence (to a casual observer). I hadn't really though about speeding them up, but then I hadn't mentally thought about speeding up the form in order to apply in to a 3 man attack (it kinda just worked with the necessary variations to accommodate the reality of the opponent, though not really very fast). I can see (carefully) practicing towards fast and fluid movements would be in line with learning the fast set (form) once you've become accomplished at all the nuances of the slow set. Perhaps shrinking the scale and increasing the speed go together?

LC:
Yes and no. Shrinking the scale condenses the energy in each transition and culmination of pose, but speed, as in time/space must come later. Shrinking the scale increases the dynamic, or smaller circles require more of the body awareness in order to avoid "cramping up" and actually shutting down the flow of energy. The entire body must be involved in small circles or one ends up just doing little curved movements. As the refinement of body skills increases, (much like a musician who has learned to play scales by "second nature" feels ready to move on to several octave runs), speed becomes more an expression of the body coiling into small circles which are endless spirals... and there is little sense of movement let alone speed to the practitioner. But to the observer, there is almost a blur of movement and the resulting "force" from such speed is a tangible reality even from across the room. This "speed" must not be a conscious construction of the player. It is a result of total familiarity with the movement(s) and careful but deliberate uncoiling and recoiling of the entire body as a continuous - thought. Now if I have lost you here I will understand. I am trying to verbalize a very non verbal situation. I find that it (the effect) is actually best understood as more of a thought than an action. Now I know this falls in with many references in the classics. It actually is quite close to descriptions I have read in various sources. Action with no action. Speed with no movement, etc. These are all subjective observations of a particular phenomenon that has as its only description - speed. But as it applies to T'ai Chi Ch'uan, it is not just fast-ness, it is actually a reality jump. You might even call it a hyper-reality jump because of the no-mind situation that it seems to employ. I know how all this must sound, but believe me I have experienced it enough times and had it observed enough times that I can safely say that shrinking the scale is only one stage. The next is no-mind or hyper-jump to fluid spiral and "it is done before anyone knows it - including you".

LC:
When my students move on to two person work they simultaneously study massage techniques, and of course are introduced to silk reeling or "Chan-ssu ching". This proves to be the true awakening period for all my students without exception. It also is the time when the true students are separated from those looking for more esoteric faldaragh. Our Chan-ssu ching is based on the Wu family drills developed I believe from the Chen influences of energy spiralling. This is also the most dangerous time for the students, since silk reeling can easily "get away" from the player and they can actually hurt themselves quite badly. This phase of their training is supervised very closely by myself and monitored constantly.

TC:
I can see (and feel!) how one could easily damage something by pushing speed ahead of control. What I feel the benefit of the exercises to be is training the spinal cord to operate the limbs, torso, etc. along their paths of least resistance and best mechanical leverage, minimizing energy expenditure and maximizing your "force to drag" ratio. Without continuous awareness and presence of mind I would expect it to be easy to literally "hit" a snag and radically torque and maybe break something. I've noticed in even form training, however, that it is difficult for many students to "get" the correct postures, muscle groups, etc. from verbal description or demonstration. Developing exercises (kungs) that work best when your posture, etc. is correct, and giving the student "things to look for" that provide internal feedback as to how well they are doing, seems to be more effective for serious students. Of course, being monitored by one of a superior skill level would be icing on the cake!

LC:
It definitely does not have any real therapeutical benefit per-se other than teaching the student how powerful (and difficult to control) the larger muscle groups can be, and how to use them to twist, jolt, and ground an opponent with relatively little expenditure of energy other than breathing, feeling and staying very very calm. My students are not taught the "Fa jing" (fast set) for at least six years into their study. The reason is the one above. They can hurt themselves very easily if it is entered into too soon without a great deal of preparation and understanding.