The Big Bang Theory

They've kissed and cuddled, and their Dungeons & Dragons characters had sex. But could Sheldon (Jim Parsons) and Amy (Mayim Bialik) finally do the deed — or perhaps even utter the L-word — in The Big Bang Theory's Valentine's Day episode, airing Feb. 6? "It is a very big, very sweet episode for Amy and Sheldon," Bialik teases.

"They have quite the romantic moment," says executive producer Steven Molaro. "It surprises them both," exec producer Bill Prady confirms.

The couple, on a double date with Howard (Simon Helberg) and Bernadette (Melissa Rauch), board a dinner train bound for Napa Valley wine country. However, it's anything but a smooth ride. "Sheldon and Amy have a rough go because he's obsessed with the train's mechanics," Helberg says. "But there are some major steps forward taken, with a pretty beautiful ending."

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