After a night dancing, Amy kisses Sheldon. It's their first kiss!
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Sheldon and Amy do a scientific evaluation when she gets turned on by Zach. They determine that she's horny. He wants her to go out with Zach, but instead she tries a hand-holding experiment with Sheldon.
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Don't look for Leonard and Priya to slow down on season five. Not even 7,500 miles can end their relationship!
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Raj and Penny looked as shocked by their actions here as viewers of The Big Bang Theory were. They slept together?!?
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Cheers to a new set up. Raj moves in with Sheldon on the season finale of The Big Bang Theory.
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Sheldon makes a grave mistake in this scene: he drinks from Leonard's glass!
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There is only one Raj.
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Sheldon busts a move on TBBT. Instant fun ensues.
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The Big Bang Theory Season 4 Quotes

Penny: Hey, Sheldon, did you change your Wi-Fi password again?
Sheldon: Yes, it's "Penny, get your own Wi-Fi." No spaces.

Raj: Well, to paraphrase Shakespeare: It's better to have loved and lost than to stay home every night and download increasingly shameful pornography.
Penny: Oh... you poor baby.
Raj: What's wrong with me, Penny?
Penny: Nothing, nothing. You know, if we weren't friends - and you hadn't brought up that creepy pornography story - I'd be on you like the speed of light squared on matter to make energy.
Raj: Hey, you totally got that right. E = MC squared.
Penny: I listen. I have no idea what it means, but I listen.