You're looking at a photo from "The Cohabitation Formulation." Raj's sister returns during the episode.
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The Big Bang Theory Season 4 Episode 16 Quotes

Just keep in mind should you ever need a slightly apathetic, tertiary friend, I stand at the ready.

Sheldon

Howard: I'm not having this conversation with you Ma!
Howard's Ma: God forbid you get one of those new fancy sex diseases!