In this second clip from tomorrow night's Supernatural, "When the Levee Breaks," Sam is being detoxed from demon blood and it seems like he hullucinates that Alistair is torturing him.
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In this first clip from Thusday's episode of Supernatural, "When the Levee Breaks," Sam is being detoxed from demon blood and thinks that Dean is ridiculing him. Very powerful scene.
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Supernatural Season 4 Episode 21 Quotes

Dean: How long is this gonna go on?
Bobby: Here, let me look it up in my demon-detox manual. Oh, wait. No one ever wrote one.

Congrats, Sammy. You just bought yourself a benchwarmer seat to the Apocalypse.

Dean