It's time to go back in time. That's what happens to Sam and Dean on the episode "The Song Remains the Same." Watch a clip from it now.
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This is a preview for "The Song Remains The Same." During the episode, Sam and Dean are sent back to 1978.
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Supernatural Season 5 Episode 13 Quotes

Dean: Well... this is it.
Sam: This is what?
Dean: Team Free Will. One ex-blood junkie, one dropout with six bucks to his name, and Mr. Comatose over there. It's awesome.
Sam: It's not funny.
Dean: I'm not laughing.

Dean: What exactly are we gonna march up there and tell 'em?
Sam: Uh, the truth.
Dean: What, that their sons are back from the future to save them from an angel gone Terminator? Come on, those movies haven't even come out yet.