And there's an amazing humanity to the show. The series' Christmas episode was a highlight, when Sheldon was so stunned by Penny's thoughtful gift that he actually hugged her — awkwardly, of course.

"It was a beautiful story," Lorre said. "I love that one. It's one of my favorites."

Both Cuoco and Parsons quickly agreed.

"It was really so fun to get to do something where Sheldon was — I mean, not only was he rendered speechless, which is a rarity, he was pushed to physicality to express an emotion he was having," Parsons said. "I mean, my (gosh), that's as close he's had to a sex scene."

Just don't expect any of these characters to change overnight. Part of the formula of keeping a successful sitcom successful is to keep the characters the same while, at the same time, allowing them to grow "oh-so slowly," Lorre said.

"All baby steps for these guys," Galecki said.

"All baby steps," Lorre agreed. "Yeah, if there's any magic trick to sitcoms — stuff happens. Nothing changes."

Just the way nothing much has changed about the sitcom format.

"If you love these characters and you are rooting for them, then situations take care of themselves," Lorre said. "So, in essence, nothing has changed. It's the same storytelling. … We put on a little play. Look, it's a couch. And then there's a kitchen. There's no bells and whistles. There's nothing we can do in editing to save it. It's right here, and this is what the audience sees (at a taping) on Tuesday night.

"And if we tell a good story about these people, maybe it's worth watching."

E-mail: pierce@desnews.com