The Big Bang Theory Season 6 Episode 18 The Contractual Obligation Implementation

Penny and Leonard get caught up in a debate over the terms of their recently updated relationship agreement. Meanwhile, Sheldon and Amy decide to take their relationship to the next level by engaging in a coitus experiment. At the same time, Howard gets into hot water when he admits to Bernadette that he doesn't enjoy watching her in her local production of "The Sound of Music." And Raj receives a mysterious invitation to participate in a secret project with renowned physicist Stephen Hawking. As tensions mount and emotions run high, the gang must navigate their way through various ups and downs in order to maintain their friendships and relationships intact. Will they be able to weather the storm and emerge stronger, or will this latest round of challenges prove to be too much for them to handle? Find out in "The Contractual Obligation Implementation," the latest episode of The Big Bang Theory.