"It's pretty insane to have James Earl Jones around at all," Jim Parsons (Sheldon Cooper) said. "He's just such an honest-to-God actor. ... There's no way ever you can even realize the amount of work he's done."
In a preview of the episode, Sheldon geeks out when he chances upon Jones in a restaurant, thanks to his legendary Star Wars role as the voice of Darth Vader.
And in real-life, Jones is a good sport about encountering die-hard Star Wars fans.
"Usually they have rows of posters they want me to sign," he told ET. "The young kids, I can't resist it. I have to do that."
Check out the video to hear why Jones is a big fan of The Big Bang Theory, and to hear Kaley Cuoco's reaction at having "the voice" at a table-reading of the script!