It's a flash mob! And it's less by Brittany in this scene from "Asian F."
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Mercedes has a moment in the cafeteria with her new man here. He is played by LaMarcus Tinker.
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Blaine and Kurt share a moment here. The scene takes place on the episode "Asian F."
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Glee Season 3 Episode 3 Quotes

It's not about doing your best anymore. It's about doing better.

Will

My alarm clock went off 30 minutes late. Sort of reshifted by whole schedule.

Mercedes