1. integument--basically, whatever protects the outside: a shell, skin, or fur on an animate creature, the shell of an egg, or the surface of a plant.
2. rictus--The sort of creepy, awful, seeming smile that people have on their face when their in the last death throes of something like the nastier poisons. Ergo, it can also be a painfully, horribly fake smile. I believe "grimace" would also work here.
3. brio--pretty much this is just another way of saying gusto.
So, there you go. Happy word hunting!