Judd Hirsch Will Play Leonard's Dad on The Big Bang Theory

The stars of The Big Bang Theory gathered at The Dolby Theater in Los Angeles Wednesday night, appearing before an enthusiastic audience at the PaleyFest fan festival. The cast, along with showrunner and executive producer Steven Molaro and co-creators/executive producers Bill Prady and Chuck Lorre, kept the audience LOL-ing while talking about the environment on set and answering questions from fans. They also revealed that we'll finally meet Leonard's (Johnny Galecki) dad, who'll be played by TV veteran Judd Hirsch.

What other gems did they share Wednesday night? Here are five standout moments:

1. New episode scoop: Fans got treated to a preview of the March 31 episode, in which Sheldon's (Jim Parsons) need for a new computer causes a big secret to come to light, which he shares with Amy (Mayim Bialik). Leonard and Howard (Simon Helberg) meanwhile, tell a white lie to Penny (Kaley Cuoco) and Bernadette (Melissa Rauch), but they're later exposed by Raj (Kunal Nayyar).

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2. Jim Parsons never saw Sheldon and Amy's hookup coming: Bialik says the cast never gets scripts until the night before their table read. When she passed Parsons in the hall she asked him if he'd read the script for when they finally go all the way. He said he asked her, "Why, do they f---?" as the audience roared laughing. It felt organic, Parsons said, even though it was unexpected. "I never thought Sheldon would have sex," he admitted. But he's come to enjoy reciting lines in bed and says he "can't wait to be in bed again."

3. Interesting wardrobe note A fan posed an interesting question: Why are the characters always wearing layers? (Sheldon is often wearing a long T-shirt under a short one, Amy loves a good vest-shirt combo, and Leonard is particularly fond of hoodies.) According to Bialik, that's the work of costume designer Mary Quigley, who ensures that the characers look like they're experiencing the seasons.

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4. Yup, they all still get nervous, even Chuck Lorre. The show is a hard and tricky thing to get right, and despite its massive success, it's not always a home run. "When it's not good," Lorre said, "you can hear the 134 freeway. It's quiet." Over the years, fans have let them know when things aren't funny, or too risqué. "It's not Two and a Half Men," Lorre notes.

5. They still get starstruck, too. Adam West 's appearance in the 200th episode was a milestone moment - especially for Bialik. "I cried when I met him," she said, later explaining that she was a huge comic book fan growing up. "That was the Batman of my youth."

The Big Bang Theory airs Thursdays at 8/7c on CBS.

(Full disclosure: TVGuide.com is owned by CBS.)