Before Sheldon learns where the chair was from, he states that it is comfortable because it supports the lumbar region and "cradles the buttocks". When Penny tells him that it was an abandoned chair she found in the street, Sheldon immediately assumes that it's unsanitary and strongly urges Penny to get rid of the chair, which she refuses. After a nightmare that involves him sitting in the chair again only to be covered with bugs, Sheldon insists that Amy try to convince Penny to get rid of the chair.
Amy tries to get Penny to get rid of it due to Sheldon's insistence, until Penny saw through his plan and told Amy to leave. Amy immediately sat in it to appease Penny, however something inside the chair bites Amy, assumed to be a rodent of some sort.
At the end of the episode, it is discovered that Penny abandoned the chair in the front of the apartment building because it is found by Howard and Raj. They decide to move it up to Sheldon's Apartment, so that Raj wouldn't have to sit on the floor so often.