Bondage.

After reading Stephanie Zacharek's glowing review of The Notorious Bettie Page, I decided to go looking for Page's photographs, hoping to have some sort of womanly-feministy ephiphany that girls seem to get from looking at burlesque/cheesecake/retro-porn. Unfortunately, the only thing that came to me was the Don Knotts observation. That, and I was surprised to see that girl-on-girl stuff was a marketable fetish even then (I'm one of those "Sex wasn't invented until the late 1960's!" people). Which led me to picture some college guy (with Steve McQueen's voice from The Blob) explaining to his girlfriend, "Aw, shucks, Sally. It's really swell when two girls kiss! It sure is neat-o!"