Can Olivia move between worlds? Walter confronts her with that question in this clip from Fringe. She then tries to take some pills to get rid of Peter... as a symptom.
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Get a sneak peek at Fringe in this clip. It depicts Walter giving a speech, passionately explaining his beliefs in the mind and the brain. He also starts to take his pants off.
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This is an early scene from the Fringe episode "The Plateau." In it, Secretary Bishop talks about the identity of Olivia and what they have to gain from this individual.
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Check out this sneak peek at the Fringe season three premiere. It features Olivia in the alternate universe, repeatedly making her case and insisting: I'm not crazy.
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Fringe Season 3 Quotes

I'm not crazy you know. To prove that to you I'd have to tell you some things that are even crazier.

Olivia

Peter: The whole time I was in there, there was only one thing I could think about.
Bolivia: Yeah what? (Peter then kisses Bolivia)
Peter: That.