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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Leonard tries to keep an affair secret from Sheldon on "The Irish Pub Formulation." This is a scene from that episode.
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Amy has a request of Sheldon on the episode "The Desperation Emanation." She wants to introduce him to her mother.
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Who needs human companionship?!? Not Sheldon, this character hopes, on the episode titled "The Zazzy Substitution."
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How can Sheldon live longer? That's what he tries to figure out on the episode "The Cruciferous Vegetable Amplification."
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Say hello to Sheldon's nemesis on The Big Bang Theory: oh, yes, it's Evil Wil Wheaton!
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Sheldon requires a chaperon on his first date when season four of The Big Bang Theory kicks off. Penny is chosen for the job.
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Sheldon has a request for Penny on the fourth season premiere of The Big Bang Theory. Will she tag along on a date with him?
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TBBT Quotes

Sheldon: Are you still mad about the sperm bank?
Leonard: No!
Sheldon: Do you want to hear an interesting thing about stairs?
Leonard: Not really.
Sheldon: If the height of a single step is off by as little as two millimeters most people will trip.
Leonard: I don't care—two millimeters?! That doesn't seem right.
Sheldon: No, it's true! I did a series of experiments when I was twelve; my father broke his clavicle.

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