The group goes all Justice League in this scene/episode of The Big Bang Theory. Seems about right for the show, doesn't it?
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A picture of Sheldon's love interest, Amy Farrah Fowler, on The Big Bang Theory.
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Sorry, it's not the best picture, but here's a photo of Bernadette from The Big Bang Theory.
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Penny, Bernadette and Amy are seen here during a night out. It's a scene from the episode "The Alien Parasite Hypothesis."
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Yes, that's Keith Carradine on The Big Bang Theory. He's played the character of Penny's dad.
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Wil Wheaton returns to The Big Bang Theory on the episode "The 21-Second Excitation." He once again causes problems for the fellas.
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Welcome to comedy, Eliza Dushku. The actress appears as a FBI agent on The Big Bang Theory episode "The Apology Insufficiency."
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Eliza Dushku guest stars on the November 4 episode of The Big Bang Theory. She plays a federal agent.
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TBBT Quotes

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

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.