Season 1, Episode 8 - The Grasshopper Experiment
Aired November 12, 2007
When Raj is set up on a blind date by his parents, he worries he won't be able to talk to his date. Meanwhile, Penny practices her bar tending skills, resulting in the discovery that Raj can talk to women with the help of alcohol.
Season 3, Episode 10 - The Gorilla Experiment
Aired December 7, 2009
When Penny wants to learn more about Leonard's work, she turns to Sheldon for lessons. Sheldon views the opportunity to teach Penny rudimentary physics as an experiment, but his teaching style quickly brings Penny to tears. Meanwhile, Howard gets jealous after his girlfriend Bernadette also takes an interest in Leonard's research.