While Kaley Cuoco has been garnering praise and accolades over the past eight months for her Golden Globe-nominated performance on the HBO Max series The Flight Attendant, there's no doubt that a huge number of TV viewers will forever think of her as The Big Bang Theory's Penny [Last Name Redacted]. And that fanbase is one that apparently has little problem approaching the highly successful actress and displaying their Big Bang Theory fandom on the spot. It sounds like everybody could use some new material, however, with Cuoco saying a ton of people end up making the exact same show reference when they see her.

Kaley Cuoco spoke with other hyper-talented Hollywood actresses such as Jean Smart, Lena Waithe, Aidy Bryant, Holly Hunter and Cristin Milioti for THR, and the group was asked what fans tend to recognize them from the most, and how they usually react in public. Everyone had great answers, with several pointing out how their voice gives their identities away before their faces do. And it's here where Cuoco mentioned the Big Bang Theory callback she gets peppered with the most. In her words:

I get a lot of people knocking at me. They’ll 'knock-knock-knock, Penny, knock-knock-knock, Penny,' multiple times. In a store, on a plane, on my body, they love to knock at me, and they think it’s very funny. [Laughs.]

For those who might somehow be unaware of what Kaley Cuoco is talking about, one of The Big Bang Theory's longest-running gags was the triple-knock from Jim Parsons' Sheldon Cooper, whose OCD tendencies were always readily apparent when making a visit to Penny's apartment. And while the show does have other catchphrases and regularly occurring bits that viewers have kept alive following the CBS sitcom's end, it's apparently Sheldon's knocking that BBT fans automatically go to when Kaley Cuoco is around.

While it's all fine and dandy that fans show their love by knocking on inanimate objects, it's probably not the best move to go up to a famous actress like Kaley Cuoco and start rapping one's knuckles against any part of her body. Even if she's fine with it in the end, maybe a TV reference isn't the best impetus to infringe on someone's personal space. Especially if the reference is the same ol' shit that everybody else is doing.

Though The Big Bang Theory went quite a few seasons without directly addressing the meaning behind Sheldon's knocking pattern, the truth did eventually surface. In the Season 10 episode "The Hot Tub Contamination," which aired in 2016, Sheldon confessed to Mayim Bialik's Amy that his over-abundant knocking goes back to a time when he was a kid and unwittingly walked in on his father having sex with another woman, which had quite the traumatizing effect on the quirky genius.

Funnily enough, The Flight Attendant featured a scene where Kaley Cuoco's character Cassie tells another character to "knock three times" when he returns to her hotel room, so that she can know it's him. However, the actress claimed after the fact that it was not an intentional callback to Sheldon, and was only coincidental.

Both The Flight Attendant and The Big Bang Theory can be streamed in full on HBO Max, though the former will hit linear TV at some point in the future. Season 2 of The Flight Attendant is currently in development, but be sure to check out all the awesome shows hitting the 2021 Summer TV schedule while waiting.

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