I only knew that because of the book about lesbian sex
that got newslettered a while back. It had the look inside feature and so I had a little read. I also didn't know that the vagina collapses closed when it doesn't have a cock/dildo/baby/aubergine in it. It seems obvious now that I know, but every diagram I've seen shows it as an open tube.
( Bob Todd whee, Mon 30 Jul 2007, 10:34, archived)