The Big Bang Theory Has A Sheldon Cooper Mistake Most Fans Completely Missed

When a show runs for a really long time, continuity mistakes and storyline errors are bound to pop up — but this one from "The Big Bang Theory" feels just a little bit egregious, to be honest. So what is it? Sheldon Cooper, as played by Jim Parsons, is supposed to be allergic to cats, but then an entire episode centers around the fact that he adopts like, a dozen cats.

At the very beginning of the series — the show's third-ever episode "The Fuzzy Boots Corollary" — it's firmly established that Sheldon is allergic to felines, which doesn't feel particularly surprising based on his character; he's obsessed with cleanliness and order, so an allergy to household pets dovetails nicely with his need for everything to be proper and perfect (we all love our pets, but they make messes).

This character trait only becomes a problem in the show's fourth season — specifically, in the season's third episode "The Zazzy Substitution" — when Sheldon, smarting from a recent breakup with his first and only girlfriend Amy Farrah Fowler (Mayim Bialik), gets a whole horde of cats as a "replacement" for his ex-girlfriend. He even names them things like Robert Oppenheimer, Otto Frisch, Enrico Fermi, and, uh, Zazzles, the last of which does not seem to be the name of a famous scientist. Sheldon's cat situation spirals so wildly out of control that his best friend Leonard Hofstadter (Johnny Galecki) gets Sheldon's mom Mary Cooper (Laurie Metcalf) involved, and the cats move out of the apartment soon after she intervenes. Still, it's weird, and far from the only egregious error you can find throughout "The Big Bang Theory" if you pay attention.

"The Big Bang Theory" ran for 12 years and as many seasons, so again, it stands to reason that the writer's room would occasionally make choices that directly contradicted events or character traits the show confirmed at an earlier point. There are still a ton of them, though; here are just a few examples.

Howard Wolowitz (Simon Helberg) would never have been permitted to go into space, which he does in season 6, as it's firmly established that he has a myriad of health issues and many of those would prevent him from becoming an astronaut. (Also, that plotline stunk; the show is better when the whole gang is together, so separating them for any lengthy period makes the show worse.) Raj Koothrappali (Kunal Nayyar) has "selective mutism" for a lot of the show, meaning that he can't talk to women unless he's extremely drunk — a questionable trait to begin with — but it ebbs and flows around Penny (Kaley Cuoco), presumably because the writers forgot and needed Raj to say something. Sheldon has some weird gaps in his encyclopedic pop culture knowledge, with the most egregious instance being that he doesn't seem to know that in "Star Wars," Mark Hamill's Luke Skywalker wields a green lightsaber. There's a whole subplot where Leonard dates a North Korean spy that has a seriously wonky timeline (and the whole thing is just incredibly weird to boot). Mayim Bialik is a cast member on the show, but in-universe, the characters talk about Bialik's show Blossom.

Still, this is all forgivable. Sitcoms go on for years and years, and not everything will always match up; hell, the same guy who played Leonard's high school bully on "The Big Bang Theory," Lance Barber, later plays Sheldon's dad on "Young Sheldon." That's movie magic for you, I guess. "The Big Bang Theory," inconsistencies and all, is streaming on Max now.