Watch The Official Big Bang Theory Podcast

Brian Thomas Smith joins Jessica Radloff to revisit his nine-season run as Zack Johnson, Penny's lovable but hilariously clueless boyfriend on "The Big Bang Theory." He shares behind-the-scenes stories from the fan-favorite Justice League Halloween episode, what it was like being the "new kid" alongside Mayim Bialik, and the kindness the cast showed him from day one. Plus, Brian reveals the storyline for an episode that was scrapped after Kaley's horseback riding accident—and what fans never got to see.

Mayim Bialik joins Jessica Radloff to look back on her first season as Amy Farrah Fowler on "The Big Bang Theory." She shares how Amy evolved over Season 4, the surprising ways she and her character are alike beyond their scientific backgrounds, and how she handled fans who initially opposed Amy and Sheldon's relationship. Plus, Mayim reflects on what it was like sharing the stage with Jim Parsons for so many years and watching one of television's most iconic partnerships come to life.

Kunal Nayyar breaks down Raj's Season 4 journey, from his bromance with Howard to Raj's unrequited feelings for Bernadette and waking up next to Penny in the finale.

Season 4 marked a turning point for "The Big Bang Theory" with the additions of Amy Farrah Fowler and Bernadette Rostenkowski, expanding the core cast to seven. Director Anthony Rich joins host Jessica Radloff to discuss the challenges — and unexpected rewards — of bringing the larger ensemble together. They also revisit fan-favorite episode "The Love Car Displacement," revealing how the memorable road trip came to life and sharing the hilarious scene that ultimately ended up on the cutting room floor.