The Big Bang Theory Season 4 Episode 20
The Herb Garden Germination
This episode revolved around gossip within the newly expanded social circle, starting when Amy tells Sheldon that she heard Bernadette was going to break up with Howard. Then, Sheldon tells Leonard. Leonard tells Priya. Priya tells Raj. Then Priya tells Leonard that Raj has a crush on Bernadette. Then, Leonard tells Penny.
The next day at lunch, Howard tells the guys that he is going to ask Bernadette to marry him.
Sheldon tells Amy about Howard's plan and they decide to scientifically test the spread of gossip. Amy tells Penny that she and Sheldon had sex and she was planting a herb garden. As they planned, the gossip about their supposed sexual encounter spreads quickly through the group, while the herb garden isn't mentioned at all.
Raj shows up to flirt with Bernadette at the restaurant, since he thinks she is breaking up with Howard. Penny finds out that Raj knows the secret, so to get his mind off Bernadette, she tells him the gossip about Sheldon and Amy having sex.
Leonard comes home and questions Sheldon about Amy to try and get him to admit he had sex with her. At a group dinner, Bernadette asks Amy about the sexual encounter, which completes the gossip circle. Sheldon and Amy celebrate the success of their experiment.
Howard gets down on one knee to propose to Bernadette. Raj is expecting her to break up with him. But, she accepts Howard's proposal, which leaves Raj in tears.