When I was a teen I used to jam with a guitar player (who had a shrine to John McLaughlin in his room) that used to play with his mouth agape all of the time. I'd roll up little pieces of paper and try to throw them in his mouth. That's what the pic above reminded me of.
My working bongo face is mouth agape. I have to consciously work at keeping it shut to avoid either catching flies or the temptation you speak of from audience members.