(( How? I've never seen the PC sit on the floor or warm themselves at a fire? ))
They are NPC animations. The instructions are actually in the beginning post to all these threads too. In a nutshell, you get a bsa extractor and open the animations bsa then extract whatever animation you wanted to try. The best way to put it back in the game is just overriding the sneak animation so you have the animation at the press of a button. Sounds like too much work? It really is.
I just tried that mod right now, and I like it a lot better. It still takes a little bit of going through it's UI though since there are so many animations with it.