Mudcatter Lorraine and I were discussing foot-tapping just yesterday (ain't it wonderful how folk music broadens your interests?) in connection with doing choruses when singing unaccompanied. It can be a great help in keeping the rhythm steady when you don't have an instrument to help keep time.Helen Schneyer often pats her knee or taps a foot and I always assumed it was to help her keep a steady beat on the slow unaccompanied songs she does.
Years ago, when I liked the rhythm of music, and if I was sitting down (don't try this if you're standing up!), I would tap both feet (alternately, that is). Friends made fun of me so I made myself stop it.... Obviously they weren't folkies.
But the last few years at the Getaway, I've noticed that Dwayne Thorpe very often taps both feet (not at the same time!) when he gets into the rhythm of a song. So I felt better about it.