OK! magazine is reporting that Mary-Kate and Ashley Olsen have a secret to obtaining their trollish smiles.

A source, who the magazine claims is close with the twins, dished, “Every time they pose and smile, they say the word “prune.”

A different source, also close to the girls, couldn’t confirm the prune story but says the twins’ smiles are important to them. “It could be true (that they say prune) but unfortunately I can’t say — they like to keep their personal lives personal. They do care about their smiles though. Mary-Kate has slightly thinner lips and more of a playful grin, while Ashley tends to go for a full-on pout. It has been the obv(ious) way to tell them apart for years.”

Stumble it!