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In this golden age of gossip blogs and behind-the-scenes Flash video footage, pop stars are hyperaware of their image, right down to those looks of utter constipation on their faces during heartfelt choruses or blazing arpeggios. They know that we know that they know. Mug makers such as John Mayer and every member of Metallica have mastered the art of the rock face, putting new twists and quivers on classic time-honored grimaces. But what exactly are they trying to tell us with those hideous glowers? We've enlisted facial-coding expert and Emotionomics author Dan Hill to help us categorize the looks and feel the pain of our pop idols.

Click here to see our guide.