Schweik, I think I know what you mean about 'twitching your face." I've seen other people do that. I think it has to do with the brain - when playing complex music, control shifts from the left front, where speech and facial expressions are controlled. Control goes to other part(s) of the brain, with the result that the face can do some very odd things.

I once saw a jazz pianist who tongue came out involuntarily. She would turn away from the crowd to hide it. A jazz guitarist I knew made some very odd grimaces. I think complex jazz causes brain activity to move from its usual hangout in the speech areas to the so-called 'lizard brain,' where hearing resides.

I have something similar. When I play piano, I can't talk.
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About the gig with the stomping - I talked to another person who was there and was really bothered by it. Also could not hear lyrics. One person got up and left at the interval. That's too bad when only ten people came in the first place.