15/20. Most of my mistakes were in the first five; I guess it just took me a few to figure out what to look for. I think it's the shaking and bobbing shoulders that are indicative of a genuine smile; it's indicative of someone who is laughing at something funny. Those who just ease into a smile without any spontaneity look fake to me.
16/20. The eyes have it, but my thought in the matter came almost exclusively from a line in the Goblet of Fire book about Karkaroff's smilte that doesn't reach his eyes. Fun to learn something actually accurate from books.