Ah, I see. Excellent stuff! In some of the asian internal arts, such as aikido or taiji, there are similar concepts to what you mentioned, jellyman. A practitioner strives to keep chi flowing through all parts of his/her body, and avoid having disruptions of the flow of chi (akin to "tension"). Ideally, at higher levels of practice, a practitioner can focus their chi on a specific area of their body so as to momentarily strengthen it (i.e. focus chi on the hand and arm when blocking a strike).
It seems that Systema also adds the interesting variable of manipulating someone else's energy as well. Extremely cool, and, at least to me, more applicable. For all I know, asian arts do this as well, but not at the beginning. The fact that Systema includes this relatively early, and couples it with a type of "awareness training" makes it a more practical application in my eyes.
David -- many of the techniques you describe seem to be almost a psychological phase of combat. I wonder if it is possible for someone to attempt to manipulate someone's density without knowing it? In grappling, I have often deliberately stared at a specific part of another person's body, in an effort to get them to defend that spot, so I can attack a different part unimpeded (I think that is similar to the JKD concept of attacking by drawing, but I am not sure). A typical example would be, while in a typical stand-up hold (i.e. hands on elbow and lapel), staring directly at the person's eyes, neck or shoulders and then executing a leg sweep. Would a deliberate feint then be a sort of density manipulation as well? You would be drawing attention to one part, while deliberately attacking another. While the first one you mention seems to be a physical manipulation, the other two seem to be mental/psychological. Sometimes mislabeled by people as "dirty tricks", actions like the ones you mentioned often give someone the opportunity to strike first in a streetfight, which is often a pretty distinct advantage.
By the way, the crotch laugh one...I'm guessing that is especially damaging to the victim's density if done by his wife or girlfriend.
