Leonard tries to keep an affair secret from Sheldon on "The Irish Pub Formulation." This is a scene from that episode.

The Big Bang Theory Season 4 Episode 6 Quotes

Leonard: You know what happens when you yawn in public...
Sheldon: Everyone will see my oddly shaped uvela.

Raj: Hands off my sister.
Sheldon: Why would I touch her? She's covered in airplane germs.