Have they tried to lip read you? I'm fascinated as to what you might be saying, if you are saying anything legible.
Do you think to yourself what you are going to play next during a piece, so you don't get to a point and forget what you should be playing and mess up? I realised I had to do that with Mozart, and I was constantly thinking to myself: "Ok, so that combination there, then that after it." Maybe you think these and your mouth almost
utters them, but not to the extent of you actually saying them.
Henrah