Season 6 of The Big Bang Theory has been marked by slowly brewing tension among the various characters. Leonard and Penny have hit another plateau in their relationship, with Leonard ready to settle down but Penny being her usual waffle-y self. meanwhile, Sheldon has spent the bulk of the season treating Amy like less of a partner and more of a pack mule, a role which until now she's been content to play. But all the tension finally bubbled to the surface this week as these two relationships hit major bumps. And it's all that damned Harry Potter's fault.