A friend ask me how to make a snake creeping but without using bones conventionally, it was too hard and slow to animate, because snakes follow an invisible path.
Here is my answer, you must to create several horizontal bones. then in frame one rotate them to create the path. The snake layer (a vector layer inside the bone layer) must be moved from one extreme of the bone chain to the other. The body has to have several points to move smoothly.

Here is a little .anme example
http://www.mediafire.com/?zmzmw1umjln
PD: I'm thinking about head deformation and have some ideas, but I have to test them.
PD2: The idea came when I saw the water glass of elbramstol, see the thread here.