One reason I like this song is because Glenn's background vocal sounds so great--a nice, warm tenor with an ever so slight vibrato towards the end of the lines. But then when I watch the '73 BBC performance, it doesn't look like he's singing. He does the oohs and humming parts, I think. At times his mouth is moving but not enough to actually look like singing. What gives--is it actually Don H I've been hearing all this time?