I have an idea. Why don't you just make the involuntary foot stampers play in their socks?

I have a theory about the faces (or lack thereof) that performers make. It says that we are used to being under the control of the higher, speech-oriented, "left-brain" areas of the brain. But when we are concentrating on music, especially fast, memorized music, other parts of the brain get to take over. And they don't care a bit what the face is doing.

This makes others, especially audience members who don't play that way, uncomfortable. They should get over it.

Also, we should always remember that the idea that the verbal, reasoning, speech-making parts of the brain are the "highest" parts originated in those parts of the brain themselves.