TV Guide TLC

Howard's fear of commitment causes him to avoid Bernadette, but he soon realises he has made a mistake and tries to compensate for it. Meanwhile, Kripke plays a prank during a radio interview with Sheldon, who sets out to get revenge, only to be caught by the Dean. Johnny Galecki, Simon Helberg and Kaley Cuoco star, with an appearance by Katee Sackhoff (Battlestar Galactica) as herself

Bernadette asks Leonard about his physics experiment, making Howard so jealous that she threatens to end their relationship. Penny also feels put out by the situation, and asks Sheldon to teach her about science. Johnny Galecki, Simon Helberg and Melissa Rauch star

Leonard's mother visits and he is horrified to learn that Sheldon knows more than he does about his own family, including his parents' impending divorce and the death of his dog. Guest starring Christine Baranski

Raj lusts after a girl he and Sheldon meet at a university party, and Leonard comes to regret airing his disapproval of Penny's belief in psychics. Comedy, starring Kunal Nayyar and Jim Parsons

Leonard and Sheldon's flat is burgled, so they work on a state-of-the-art security system in a bid to outwit any future would-be thieves. However, their plans go awry when they ensnare Penny in a net. Comedy, starring Johnny Galecki and Jim Parsons

Sheldon develops a mental block and has difficulty working on a formula, so in a move inspired by Albert Einstein he gets a job at the Cheesecake Factory diner to try to revive his creativity - and despite Penny's objections, proves surprisingly effective in the role. Guest starring Yeardley Smith (The voice of Lisa Simpson)