When I started working on the tail, I had to research the actual movement first.
http://www.youtube.com/watch?v=VSxhN6qhAXUReally, the tail should be even more stiff, but I REALLY didn't want to do that.
fortunato, the mouth is a little jerky at the moment. I'll add that to the list.
Dex, I'll certainly be adding more detail, as I want the the rat to appear more grotesque; I might even expose the skull. We'll see!
As for the speed, he is moving a bit slow, but it's already running at, I believe, slightly under 30 fps. (At least, it SHOULD be. Perhaps your browser is slowing it down...?)