I think Fishbed has hit the nail on the head. A windsock may look like a venturi tube, but the air in it doesn't act like it was in a venturi. I think that it is a consticted pipe. Put your finger over a hosepipe and let a little of the water out, what happens is an increased outlet pressure and an inflated hosepipe, same as a windsock.
[ 26 February 2002: Message edited by: weirdy ]</p>