The Big Bang Theory-S01E5 Video

'The Hamburger Postulate'
While eating at the Cheesecake Factory where Penny works, the guys run into Leslie Winkle (Sara Gilbert) and she suggests that Leonard play in her string quartet as they are in need of a new cellist as the other players are uncomfortable near the other guy due to the chance he was irradiated at work. Later, after the practice in Leonard and Sheldon's apartment, Leslie offers herself to Leonard and they have s*x.

Meanwhile, Sheldon is uneasy as to how to act after realizing Leslie slept with Leonard. Later on, Penny congratulates Leonard, and he tries to figure out what Penny's words meant. Leonard eventually decides to pursue a real relationship with Leslie over an imaginary one with Penny. However, when Leonard arrives in the lab, Leslie makes it clear she is not interested in a relationship, and only used him to satisfy her s*x drive. Leonard later tells Penny, who walks away with a smile on her face, seemingly happy to hear this news.

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