Season 5, Episode 2 - The Infestation Hypothesis
Aired September 22, 2011
When Penny takes in furniture she found in the street, germophobe Sheldon is horrified and urges Penny to remove the chair from the building. Amy finds herself caught in the middle of the argument between Sheldon and Penny. Meanwhile, Leonard is still adjusting to his long-distance relationship with Priya and tries to spice things up between them.