Season 9, Episode 17 - The Celebration Experimentation
Aired February 25, 2016
After more than nine years together, the gang finally celebrates Sheldon's birthday, surprising him with a special guest, on the 200th episode of The Big Bang Theory.
Season 10, Episode 4 - The Cohabitation Experimentation
Aired October 10, 2016
After Amy's apartment is flooded, Penny suggests that Amy move into Apartment 4A with Sheldon. Unsure about finally cohabiting with his girlfriend, Sheldon comes around to the idea when he looks at it as a five week experiment in living together. Sheldon suggests they move into Penny's old place, Apartment 4B, so they would know if he's comfortable because he's living with Amy and not just comfortable in his own apartment.
Meanwhile, Howard and Bernadette decide not to learn the gender of their baby, but they question their decision when Raj reveals that he knows the sex of the baby.