Smiling helps the immune system to work better. When you smile, immune function improves possibly because you are more relaxed. Prevent the flu and colds by smiling. One more reason to flash those beautiful teeth!
I actually really like Emma Stone, but being a redhead (or at least often-dyed-red-head) with a crazy gleam in her eye, she'd do a good job as the psychotically deadly Krystal who joins Thanatos in book 2 (Underworld's Daughter).