According to Sheldon, Leslie Winkle shaved her legs in winter thus signaling sexual availability.
Leonard proposes an experiment to Leslie:
A bio-social exploration with a neuro-chemical overlay. (In layman's terms: let's study the changes in the brain that occur when a human man and woman interact with each other).
Characterized as the modification of our colleague/friendship paradigm with the addition of a date-like component.
The generally accepted pattern in this area: I pick you up, take you to a restaurant, then we would see a movie. Probably a romantic comedy featuring the talents of Hugh Grant or Sandra Bullock.
It was agreed that the primary way we would evaluate either the success or failure of the date would be on the biochemical reaction during the goodnight kiss. Heart rate, pheromones etc.
Leslie proposes stipulating that the date goes well and move to the key variable.
Kiss each other now.
Leslie defines the parameters of the kiss: closed mouth but romantic.
Leslie presents her findings: it was a good kiss, reasonable technique, no extraneous spittle. On the other hand, no arousal.
Leonard: we tried kissing but the earth didn't move.
S01:E03
Leslie runs into Leonard and the gang at the Cheesecake Factory and tells him that the Physics Department string quartet needs a new cellist after Elliott Wong switched over to high-energy radiation research, had a little mishap and now the other guys are uncomfortable sitting next to him. After Leonard agrees to join the string quartet, he is informed that they will rehearse on Tuesdays at his place after the Department of Energy said their regular rehearsal spot is kind of a hot zone.
During rehearsal, Leslie sees Leonard handling that beautiful piece of wood between his legs (obvious crude double entendre) and starts flirting with Leonard in an attempt to seduce him:
~ I admire your fingering
~ Maybe sometime you can try that on my instrument
After rehearsal ends and the other two players leave Leonard's apartment, Leslie hangs back and offers to practise that middle section again as a pretext for letting Leonard know that she is sexually available.
Musical foreplay.
After spending a great night together, Leslie doesn't appear to be interested in dating and rather uses men as tools for stress release.
S01:E05
In the Caltech cafeteria, Leslie approaches Leonard after she heard that his relationship with Penny crashed to the ground like blue ice falling out of an airplane lavatory.
Now that Leonard is unattached, Leslie proposes revisiting their previous attachment.
Leslie explains that she is all done with casual sex and is fully committed to the traditional relationship paradigm.
Leslie suggests they proceed by going to Leonard's place; order Chinese takeaway; rent a movie, artsy but accessible then light petting, no coitus.
Leslie says it's better for Leonard to assume the male role and will leave the details to him.
Whilst eating orange chicken from Chang's, Leslie asks Leonard how many children he thinks they should have and what genetic weaknesses run in his family (shortness, lactose intolerance, male pattern baldness).
They agree to postpone intercourse until their relationship is past the initial viability test.
Leslie reminds Leonard that protocol dictates that he waits a minimum of 18 hours before calling so that she is not repulsed by his cloying eagerness.
During Leonard and Leslie's second date, an argument ensues between Leslie and Sheldon. Leslie strongly believes that only loop quantum gravity calculates the entropy of black holes. Sheldon believes that string theory and that matter clearly consists of tiny strings.
Leslie asks Leonard whether he agrees that loop quantum gravity is the future of physics.
Leonard says he prefers his space stringy, not loopy.
Even though they are talking about untested hypotheses and whilst Leslie could have accepted their kids being genetically unable to eat ice-cream or ever get a good view of a parade, but Leonard not agreeing with her theory is a deal breaker.
S02:E02
Whilst seeking shelter in the paintball shed, Leslie and Howard Wolowitz start a 'friends with benefits' arrangement whereby Leslie controls Howard with new expensive equipment and research trips in exchange for sex. In other words, Howard is a bought and paid for sex toy and arm candy.
Leslie got grant approval for a rapid prototyper for Howard.
Leslie also got Howard onto the research trip to Geneva to check out the CERN super collider in exchange for Howard accompanying her to her sister's black tie wedding.
S02:E16
Leslie dumps Howard over the phone: "Howard, Mama's a rolling stone."
Howard has an emotional response when he was meant to be in a non-emotional relationship. Howard obviously had feelings for Leslie because he saw her naked.
S02:E21
After a drunken and lonely Penny uses Leonard for a one-off night of sex and walks out on him, Leonard goes to Leslie's apartment (18 months after they stopped dating) and suggests they start having recreational, meaningless sex again for a bit of fun.
Leslie says to let her think about it and slams the door on Leonard.
S03:E23
