It's not. Someone from Deviant Art did it if I'm not mistaken. They splice 2 vid clips together. If you look by her left shoulder (our right) you can still see what looks to be part of another person behind the one groping herself. Also, the lock of hair by her right collarbone and where her arm attaches to her torso lengthens, and there's a light reflection on her neck that disappears even though the shadow made by her head moving down doesn't hit that area.