Butt Shaking flash animation program?

[MASKOAA]

I remember being on a site with a link that said something along the lines of HOW TO KEEP A GUY OCCUPIED so I clicked it and it was a picture of a girl with her has and you can click on her ass and drag it were you want on the screen and let go and it would sorta dance.....does anyone know how they did that I? I want to be able to do that with whatever picture I want.