Being the little nut job that he is, Sheldon runs a few tests after Penny comes back from Nebraska with a cold.
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Sheldon and Leonard both sit together sick on the couch with no one to take care of them.
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When Penny brings a cold back from Nebraska that she gives to Sheldon, she's stuck taking care of him when no one else will.
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Sheldon hires some guy to pose as his cousin, Leo, to pretend to need an intervention for Sheldon to avoid going to see Penny in Rent.
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Sheldon has one of his co-workers post as his non-existent cousin, Leo, in order to get out of seeing Penny in Rent.
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Leonard attempts to talk his way out of going to see Penny in Rent after hearing her sing off key.
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Sheldon hides in stealth in the crowd during Leonard's presentation. Very incognito.
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Penny falls asleep when she, Wolowitz and Raj go to listen to Leonard give a presentation.
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Sheldon tries to attack Leonard with his mind when he goes to give a presentation that Sheldon does not approve of.
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Raj and Sheldon get into an argument when Raj is out on his blind date. Guess who she goes home with?
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Penny uses Raj and the guys as her test subjects as she practices making drinks. Here's a pic of her getting Raj liquored up.
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Penny practices bar tending on the boys in order to learn up for her new job that will help earn her some extra cash.
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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: Hey, Sheldon, did you change your Wi-Fi password again?
Sheldon: Yes, it's "Penny, get your own Wi-Fi." No spaces.