The big letters in the background say it all here. Glee is paying tribute on "Michael" to, well, Michael Jackson.
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The Glee gang makes like MJ in this scene from "Michael." They are singing a classic King of Pop single.
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The Glee cast all takes to the stage in this shot from "Michael." It's the show's tribute to the King of Pop.
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Glee Season 3 Episode 11 Quotes

I'd throw this mocha in your face, but it's not nearly scalding enough.

Santana

I don't want to see the spectacle that is Michael. I want to be the spectacle that is Michael.

Mercedes