Brittany, Quinn and Tina are shown here in a scene from the episode "Furt." They are listening to a speech from Rachel.
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Rachel and Santana are seen here in the episode "Furt." They are discussing a plan to help Kurt.
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Yes, that's comedic legend Carol Burnett on Glee. She plays Sue's mother on the episode "Furt."
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Glee Season 2 Episode 8 Quotes

We're gonna go to the hotel where they put up the guest stars on Lost.

Burt

Carol: We wanted the two of you to be the first to know.
Burt: Yeah, after the kids in that home room.