I'm sure plenty of you guys know this situation well: Someone's playing some blues guitar lick, and right as things get real stanky, they make a weird face, seemingly in reaction to the lick they're playing (some seem to be unable to avoid doing this, actually, and still others do it on purpose!). My questions are asking when and how this tradition got started.
There's another question that kind of gets at this a little in its answers, but are there any explanations as to why this occurs?
Do we know whether early blues pioneers did this when they played, or is this a relatively recent development?
This facial twist occurs in other contexts/genres, too, especially during difficult passages. Is there any record of this being observed for other styles in the past? (the western musical tradition has a bunch of recorded history for classical music, so maybe there?)