Simon Helberg, Johnny Galecki, Kunal Nayyar and Jim Parsons, The Big Bang Theory

A funny thing happened last week. A quiet little comedy that neither stars Charlie Sheen nor teases us with the identity of a proverbial Mother hit a ratings milestone (9.9 million viewers), putting a certain behemoth of a dance competition to shame in the process. Yep, we're talking about CBS' The Big Bang Theory (Mondays at 8 pm/ET), which in its second season is proving to be one of the most reliable laugh generators on all of prime time.

Of course, that's not to say it's immune to the occasional sweeps stunt. Bill Prady (who cocreated the comedy with Chuck Lorre) shared with TVGuide.com a look at how some Top Models get wrapped up in our boy geniuses' world, as well as reveals the show's overall formula for success. (Thankfully, it does not involve string theory.)

TVGuide.com: Congratulations on the series-high ratings. Is the 10 million threshold in your sights?
Bill Prady: I've got to tell you, I was waiting for when we beat Dancing with the Stars in the demo, which we did. That was sort of my goal. And it felt really good!

TVGuide.com: What's great is that as the series surges, you're not doing anything different. You haven't dumbed it down or "made it more accessible." It is what it's always been.
Prady: I think we only know how to do this. [Laughs] It's interesting because the thing we're here to talk about, it didn't start out as, "How can we do a stunt with Top Model?" It was just a storyline we pitched that seemed natural to the characters. We work inside-out that way.

TVGuide.com: What are the Top Model gals doing, and who are they doing it with?
Prady: They are the object of a quest. Penny's television is on the fritz, so she comes next door to see who's being kicked off of America's Next Top Model. When Penny lets it slip that all the women live in a house together, Wolozitz is taken aback. He realizes that once a week, a beautiful girl is kicked out of this house, left with no self esteem — aka the Future Mrs. Howard Wolowitz. [Laughs] So he and Koothrappali use science to try to locate the house, charting star positions and physical landmarks, using satellite photography....

TVGuide.com: I've always thought it'd be fun if Wolowitz got a steady girlfriend for a few episodes.
Prady: He will, at some point. Coming up, he is going to meet a girl played by Sara Rue, and Leonard will steal her away — though he won't mean to do it.

TVGuide.com: Going into the first season finale, did you have any intention of following through on the Penny-Leonard romance? Or was it always just a tease?
Prady: [In an early draft] they did not go out at the end of it, and it felt so unsatisfying. People said, "Careful, there are many sharks waiting to be jumped if they [have a date]," but we felt that if we were honest to the characters, the first time simply wouldn't go well. And they won't try it again for a while. My feeling is that the reality of that guy, with that girl, will start and stop over the years. This is of course the nerdiest writers room in television, and we've all brought our experiences of being nerds who loved pretty girls. What happens is you take a shot, you screw it up, you back off, time passes, you take a shot again.... Penny's not yet at the place in her life where she has figured out that the Leonards of the world are better for her than the Biffs. But she'll get there, someday. The thing that was very exciting is that it was Penny's problem [she never graduated college] that prevented the relationship. And once we found out it was Penny's problem, Leonard screwed it up massively. [Laughs]

TVGuide.com: Fans also love the scenes with Sheldon and Penny. Does that present a tricky balancing act?
Prady: When we have a story and it's fun, we do it. [This week] things come to a head between them, and the ending is surprising as to who gets the upper hand and why. It's like an earthquake — you have tremors, an earthquake, and then it's gone for a while.

TVGuide.com: Sara Gilbert is a regular this season, yet we haven't seen much of Leslie Winkle. Will that change soon?
Prady:
She's in an episode coming up. Being a semi-regular, I think, is her actual arrangement.

TVGuide.com: Some fans think Sheldon might hook up with Leslie before Leonard does.
Prady:
In last week's episode Penny asked, "What's Sheldon's' deal? Is it guys, girls, sock puppets...?" The guys say, "We've been operating under the assumption that Sheldon has no deal." Sheldon is so far away from having any kind of human relationship, I don't think he is a big contender.

TVGuide.com: Settle a small mystery here: Who's the voice of Wolowitz's mom?
Prady:
Carol Ann Susi. She's a terrific actress, and we think it's delightful that we don't see her. Carol Ann says [adopting her raspy, accented voice], "I don't have to dress up or put on makeup. This is the best job in television!"

TVGuide.com: Are we going to meet any more characters' family members this season?
Prady:
Leonard's mom might come to visit. We're still figuring out what kind of woman she would be. We've established that his father is an anthropologist and his mother is a research psychiatrist. We've often said there's the possibility that Leonard is the least successful in his family. His parents always pushed him toward academic success, whereas Sheldon's parents had no idea what had been born among then. [Laughs]

TVGuide.com: Your episode titles are all written in the form of a "theorem," "hypothesis," "paradigm".... Any fear of running out?
Prady:
It was a very big issue at the start of the year, whether we could reuse words. The official belief is that we will reuse them each season — because there aren't 250 different ones.

TVGuide.com: If you ever want a good groan, check out Knight Rider's episode titles. They all use a pun on the word "night."
Prady: As long as they do an episode called "Good Knight, Moon," I'm happy!