Can you spot fake and genuine smiles?

Another of those interesting online quiz things - this time to assess how well you can tell a fake from a genuine smile, and vice versa.

I got 15 out of 20 correct, perhaps slightly better than I thought I might get - but still with enough mistakes to realise I can be fooled rather too often. Of the five I got wrong, 2 were genuine smiles that I thought were fake, 3 were fake smiles that I thought genuine.

(thru Rachel from north London)