I agree with all that's been said. And thanks for the original question. My two cent summary is:
1.) Unpredictability: Continuous variation in speed, pressure and motion. Mix together pokes and strokes. Maker the 'lee build, ease off, build, ease off -- sometimes changing gradually, but sometimes suddenly -- going back to previous spots without warning. You must make them lose the ability to predict you.
2.) Always make them talk: Getting inside their head means you're asking questions, teasing, and making them try to think, talk and answer, while at the same time taking control of their nerve reflexes. The physical breaks down much more, if you undermine their psychology. And emphasizing verbally how involuntarily they're reacting makes it clear you're more in control of their reactions than they are.
3.) Learn: Study and compare their reactions to different kinds of touches like a scientist. (This can be part of what you talk about as you're doing it.) Never just keep to your own standard, usual, pre-set course.
4.) Play with 'The Line': Make it clear to them that you're managing some sort of line that's short of their total madness, and they will accept your authority much more fully. It actually matters less where you decide to drive the line, regarding intensity, than that you've drawn it somewhere.
(I'll probably want to come back and re-read this whole thread before my next session.
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