Photo SpecialStars In Masks!

Who's that pig? See Keira Knightley and other stars (Britney! Celine!) wearing wacky masks

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The actress and her friends hammed it up for Knightley's 21st birthday party at London's Café Royal.

Credit: Ramey; Matrix/Bauer-Griffin

Updated: Thursday Apr 10, 2008 | 06:00 AM EDT

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