The secret behind those enigmatic half smile/half grimaces? We found out this year …

It’s prunes!

“Every time they pose and smile, they say the word ‘prune’.”

Who knew? That prunes are good for more than just poo?

Mary Kate and Ashley Olsen figured it out – this is why they’re always so puckered.

One of the best stories this year. Pruning and posing. It totally works!

Photos from Wenn.com