Tonight, I got expressions working on the skull model. Check out Yorick's "angry face":
You can see in the shot that Yorick's "eyebrows" have turned into a "V" shape, suggesting anger.
This shot also shows some really over-the-top lighting for the angry face. I'm thinking of having the lighting change when he gets mad; the red tinting and the glowing green in the skull would not normally be there, so that when he burns into angry mode, he looks really pissed.