Penny comes to Sheldon for help to better understand Leonard's work and here he is training her.
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We love any scene involving Sheldon and Penny together and here he is taking her to the hospital when she's injured.
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With Leonard gone, Sheldon helps an injured Penny. She looks a little loopy here.
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Leonard and Penny act as parents as they go to pick up Sheldon from the comic book store.
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Sheldon comes to visit Penny at work at the Cheesecake Factory to try and convince her to apologize to Leonard to stop the fighting.
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Penny joins the nerds in a friendly game of cards. Here's a cute picture of her smiling as Leonard look at her.
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We sure see a lot of Penny and Leonard in bed. Not that were complaining, this is where we want to see this couple!
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When Penny spends the night at Leonard's she ends up ruining oatmeal day by cooking french toast. How dare she?
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TBBT Quotes

Penny: Here's a question-- as an alien pretending to be human, are you planning to engage in any post-prom mating rituals with Amy?
Sheldon: There are post-prom mating rituals?
Penny: Not always. Unless your date drives a van with an air mattress, then always.
Sheldon: Well, if it's part of the prom experience, then I'm open to it.
Penny: You're kidding.
Sheldon: I may be an alien, but I have urges.If Amy wants to copulate by firing her eggs into space, well, then, I will happily catch them with the reproductive sac on my upper flermin. I'm not the best at reading facial cues, but I can see that you're a little turned on.

Penny, there's only one cookie with something in the middle that solves life's problems, and that's an Oreo. Or a Nutter Butter, if you're in a pinch.

Sheldon