Although "The Big Bang Theory" is relatively mild and family-friendly, at least compared to its contemporaries like "How I Met Your Mother" or "Modern Family", it regularly delved into sexual humor. Howard always has a joke to tell and he does there is no shortage of jokes about Penny's sex life. However, with Sheldon (Jim Parsons), the show was borderline G-rated; the character had seemingly zero interest in sex for the first few seasons, and even by the end of the show, evidence of his libido was still few and far between. On Introducing Amy (Mayim Bialik) in the season 3 finale helped define him as heterosexual, though that label of Sheldon's sexuality will always have a huge asterisk next to it.

Sheldon's lack of interest or awareness of sex is what helped a risqué joke in season six's "The Fish Guts Displacement" work so well. His story involves Amy pretending to be sick to trick him into being more intimate with her. He eventually discovers the deception, so Amy convinces him that some kind of punishment is necessary. Thus became the famous scene where Sheldon hits Amy, unaware of the fact that Amy does not consider it a punishment at all.

It's a scene that could have been creepy, but it works because of how sexless Sheldon (and to a slightly lesser extent, Amy) has been throughout the show. However, it was difficult for the actors, partly because they couldn't stop laughing the whole time.

"I'd say it's one of the hardest things I've ever had to do because I thought it was so much fun," Parsons said in a 2013 panel. The scene was originally supposed to be shot off-camera, with a shot of Amy's monkey reacts to the sight serving as a stage punch, so a last-minute change complicated things a bit.

"I was pissed off, because I was like, 'Well hell, I'd have been practicing how to control myself if I'd known all week,' but I've been slapping my ass off camera all week," Parsons said. He added of Bialik, sitting next to him: "You have no idea how she plays."

At the same panel, Bialik joked that "there was some redness" after filming the scene, due to the multiple takes. Parsons joked that the punching had to be realistic "to get the sound we want," adding, "It's all in the name of art."

In another interview for Jessica Radloff's 2022 book "The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series" Parsons elaborated a bit more on the experience, explaining what the last-minute scene change felt like: “I was spitting nails, I was so angry at these people for putting me on camera... and I couldn't quit. laughing, which just pissed me off because I suddenly couldn't do my job."

The scene at the end was one of the most memorable parts of the entire series, referenced and many fan memes. And there must have been something in the air around Hollywood at the time, because the animated sitcom "American Dad" pulled off a very similar sequence in its spring 2013 episode, "The Missing Kink," which aired just a few months later. That episode featured housewife Francine (voice of Wendy Schall) tricking her husband Stan (Seth MacFarlane) into beating her, with stern, no-nonsense Stan not quite understanding the situation.

Of course, the version of the story we got on The Big Bang Theory was the more memorable of the two, as its live-action format meant the actors had to put a lot more on the line. It was a risky scene for Bialik and Parsons — maybe not as risky as The BDSM scene that got The Big Bang Theory episode banned in the UKbut still — and as far as "TBBT" fans are concerned, the gamble paid off.