Penny and Sheldon sit outside the apartment and talk while Leonard takes over the apartment for his date with Leslie.
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Leonard comes home to find out the guys spied on how his date with Penny went via a webcam they put in the hallway.
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Penny tells poor Sheldon a secret whether he wants to hear it or not. Unfortunately that secret involves Leonard and puts him in a difficult situation.
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Penny and Leonard return from their first date and Penny tells Leonard she wants to take it slow. Poor guy.
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Sheldon attempts to befriend Kripke in order to use his super computer at work. As a result, Sheldon is forced to go rock climbing and isn't too happy with the height.
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Penny hugs Leonard after he does his best to comfort her after he ex reveals intimate details about her on his blog.
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Wolowitz teaches Sheldon Mandarin so he can correctly order his Chinese food to make sure he gets tangerine instead of orange chicken. Makes sense to us.
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Leonard and Penny are about to kiss in this still. Leonard finally asked out Penny on a real date after she was hurt by her ex.
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Penny tries to organize a surprise party for Leonard with his friends Sheldon, Howard and Raj.
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Penny makes Sheldon go to a computer store to pick out a gift for Leonard for his birthday but he ends up very distracted.
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Wolowitz uses his peanut allergy to try and distract Leonard long enough for Penny and the gang to set up her surprise party.
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The boys all end up competing for Sheldon's sister, Missy's affection. Raj and Wolowitz even get into a physical fight.
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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.

Sheldon: Why do you have the Chinese character for "soup" tattooed on your right buttock?
Penny: It's not "soup," it's "courage."
Sheldon: No it isn't. But I suppose it does take courage to demonstrate that kind of commitment to soup.
Penny: How'd you see it? You said you wouldn't look.
Sheldon: Sorry. As I told you, the hero always peeks.