Interesting fact:

“I was glad my father was an eye-smiler. It meant he never gave me a fake smile because it's impossible to make your eyes twinkle if you aren't feeling twinkly yourself. A mouth-smile is different. You can fake a mouth-smile any time you want, simply by moving your lips. I've also learned that a real mouth-smile always has an eye-smile to go with it. So watch out, I say, when someone smiles at you but his eyes stay the same. It's sure to be a phony.” ― Roald Dahl, Danny the Champion of the World