Penny comes to Sheldon for help to better understand Leonard's work and here he is training her.
Bernadette (Melissa Rauch) joins the guys for lunch at work as she begins to bond with Leonard over his work.
Wolowitz confronts Leonard when he gets jealous over his friend bonding with his girlfriend, Bernadette.
Raj and Sheldon race... with a little Mario Kart on the Wii.
Wolowitz gets jealous when Leonard and his girlfriend Bernadette (Melissa Rauch) get friendly.

The Big Bang Theory Season 3 Episode 10 Quotes

Sheldon: Why are you crying?
Penny: Because I'm stupid!
Sheldon: Well that's no reason to cry; one cries because one is sad. For example, I cry because others are stupid and it makes me sad.

Sheldon: Where's your notebook?
Penny: I don't have one.
Sheldon: How are you gonna take notes without a notebook?
Penny: I have to take notes?
Sheldon: How else are you gonna study for the tests?
Penny: There's gonna be a test?
Sheldon: Tests. Here, it's college ruled, I hope that's not too intimidating.