'Big Bang Theory' Flash Mob Choreographer Briana Cuoco Spills on Those Behind-the-Scenes Dances! (Exclusive)

Also, find out which actor needed notecards to learn all the moves!

Kaley Cuoco's sister, Briana Cuoco, is cluing in Big Bang Theory fans on which of the cast has the fanciest footwork!

ET's Keltie Knight caught up with the actress in L.A. on Wednesday, where she discussed choreographing all three of the flash mobs which went down on the show's set over the years, and it turns out some of the stars are born dancers.

"You know who kinda kills? It is Mayim [Bialik]," she reveals. "Mayim slays it! And Kunal [Nayyar]."

She also shared that at least one actor embraced their character's nerdy habits in order to get the routine down.

"I will say that Jim [Parsons] had flash cards," she says. "He would write down all the choreography on flash cards…. I swear! But then he felt a little FOMO and needed to get into the next ones."

Briana also chatted about whether or not her sister and her husband, Karl Cook, are any closer to parenthood these days. "They're so happy, I don't think kids are for a while for them. I think she just wants to enjoy being married," she says.

Briana is also hard at work crafting her very own line of fitspo apparel called Cult, which will be available later this year.

When Knight joked that Briana already has a huge celeb (her sister) to help her promote the line, she responded, "That's correct and I will use it for all it's worth!"

The Big Bang Theory's hour-long finale airs Thursday, May 16 at 8 p.m. ET/PT on CBS.

Check out the full chat up above.