Leslie: Listen, Leonard, neither of us are neuroscientists but we both understand the biochemistry of sex. I mean, dopamine in our brains is released across synapses causing pleasure. You stick electrodes in a rat's brain, give him an orgasm button, he'll push that thing until he starves to death.
Leonard: Who wouldn't?
Leslie: Well, the only difference between us and a rat is that you can't stick an electrode in our hypothalamus. That's where you come in.
Leonard: Yeah, well, I'm just glad to be a part of it. So what happens now?
Leslie: Well, I don't know about your sex drive, but I'm probably good till New Years.