[s4e20] The Herb Garden Germination -

: Refers to the mundane "control" rumor Sheldon and Amy used for their social experiment.

: After hearing a rumor from Penny that Bernadette is considering breaking up with Howard, Sheldon and Amy decide to study "memetic epidemiology". They intentionally plant two rumors to see which spreads faster: a salacious one (that they had sex) and a mundane one (that they are starting a herb garden). [S4E20] The Herb Garden Germination

: Renowned physicist Brian Greene appears as himself, giving a book reading that Sheldon and Amy attend specifically to heckle. : Refers to the mundane "control" rumor Sheldon

: The engagement is particularly devastating for Raj, who had been harboring a secret crush on Bernadette and was hoping the breakup rumor was true. Key Episode Details [S4E20] The Herb Garden Germination