The physics engine in The Creation Engine (Skyrim's custom game engine designed by Bethesda) is very bare bones. It's pretty much limited to actors falling and weapons and otrher items reacting to touch. Well, with this Skyrim Script Extender plugin, that fact is thrown out the window. This mod taps into the games' physics and applies it to other things, such as hair, capes and breasts. It's very neat to watch.