While The Big Bang Theory’s cast was one of the best lineups in recent sitcom memory, the show’s casting process involved some strange coincidences, odd choices, and weird paradoxes. The Big Bang Theory was a hugely successful sitcom, and it was the type of series that lived or died by the strength of its cast chemistry. Some sitcoms like Community and 30 Rock played with the genre’s conventions via clever meta-humor. Other entries into the genre, like New Girl and Brooklyn Nine-Nine, used romance to drive the action. While The Big Bang Theory had its share of romances and meta-jokes, these weren’t the show’s primary appeal.

The Big Bang Theory was a traditional, multi-camera hangout show in the mol of Friends or Seinfeld, and the series focused its attention on the interplay between its main actors. The Big Bang Theory’s most watched episodes raked in tens of millions of viewers, proving that this strategy was a successful one. While the show’s plotting was never too dense and the storylines unfolded at a leisurely pace, most audience members tuned in each week to see Sheldon, Leonard, Penny, Raj, Howard, Bernadette, and Amy trade one-liners. However, while The Big Bang Theory benefited from a stellar lineup, its casting process involved some weird secrets.

7.Jerry O’Connell Is Younger Than Jim Parsons (Despite Playing His Older Brother)

Even though Stand By Me star Jerry O’Connell played Sheldon’s older brother, Georgie, in The Big Bang Theory season 11, episode 23, “The Sibling Realignment,” the actor is actually a year younger than Sheldon actor Jim Parsons. This was not particularly noticeable in The Big Bang Theory episode, as Parsons has a youthful face. However, it became much more obvious when the show’s spinoff Young Sheldon began airing years later. Young Sheldon is almost as popular as its predecessor, but it is hard to ignore the fact that Georgie is years older than his brother in the spinoff, even though their original incarnations look the same age.

6.The Same Actor Played Two Different Characters

The Big Bang Theory featured a lot of one-off characters, but surprisingly enough, the show once got the same actor to play two unrelated characters in two separate episodes. In The Big Bang Theory season 3, episode 3, “The Gothowitz Deviation,” Morgan portrayed the Goth girl Howard tried to impress. Meanwhile, in The Big Bang Theory season 8, episode 16, “The Intimacy Acceleration,” she appeared as an intense escape room host. The fact that both these characters shared an interest in the spookier side of life made it possible that they were intended to be the same person. However, this probably wasn’t the case, as Raj didn’t recognize Morgan’s character.

5.Sara Gilbert’s TBBT Casting Reunited An Iconic Sitcom Couple

Future The Conners star and sitcom legend Sara Gilbert played Leslie Winkle, Leonard’s short-lived love interest, in The Big Bang Theory. Gilbert and Leonard’s actor Johnny Galecki previously played the couple Darlene and David in the hit ‘90s sitcom Roseanne, which ended with the pair happily married and raising their first child. However, in The Big Bang Theory, Leonard’s interest in Penny ensured that their romantic reunion didn’t last. This time around, Gilbert and Galecki’s characters only dated for a few episodes before parting ways. Winkle continued to appear throughout the series, while The Conners brought back Galecki to reveal that Darlene and David’s marriage didn’t last.

4.Sheldon’s Twin Is Actually Younger Than Him

While Georgie’s actor was a year younger than his brother Sheldon, Sheldon’s twin sister Missy had an even more egregious age gap with the actor. Missy actor Courtney Henggeler is six years younger than Parsons despite the fact that Sheldon and Missy are canonically twins. However, this was not particularly noticeable since Sheldon’s actor scarcely looks his age in real life. Parsons’s strikingly young appearance complicated the casting of the series numerous other times, with his on-screen mother, Laurie Metcalf, being only 18 years older than him. However, that was not the oddest thing about Mary’s casting in The Big Bang Theory and its later spinoff.

3.Young Mary Cooper Is Played By The Actress’s Real-Life Daughter

The Big Bang Theory’s spinoff Young Sheldon kept one sitcom tradition alive by casting Metcalf’s real daughter, Zoe Perry, as its younger version of Mary Cooper. This was an ingenious move since the spinoff’s iteration of Mary isn’t very similar to her incarnation in The Big Bang Theory. As a result, the obvious visual similarity between the two characters reassures viewers that she is still the same Mary Cooper, even if she is much more naive and less bitter. Viewers can reasonably assume that the death of Mary’s husband led to the increased pettiness and mean-spirited remarks from Metcalf’s older version of The Big Bang Theory character.

2.Amy’s TBBT Casting Created An In-Universe Paradox

‘90s child star Mayim Bialik was mentioned in an episode where Raj suggested inviting the Blossom actor to join the group’s bowling team. This is notable because a few years later, Bialik went on to join the cast of the series as Sheldon’s love interest, Amy Farrah Fowler. This was not the first time that a sitcom accidentally created an in-universe paradox involving its actors, as How I Met Your Mother once created a Jason Segel paradox with a scene wherein Marshall stood in front of a poster for Bad Teacher, a movie that starred the real-life actor. However, Blossom shared even more bizarre connections with The Big Bang Theory.

1.Johnny Galecki Was Mayim Bialik’s First Kiss Before TBBT

Galecki played Bialik’s love interest in an episode of Blossom and gave the character — and her real-life actor — her first kiss. This became a strange coincidence decades later, when the duo were reunited as Leonard and Amy in The Big Bang Theory. Although Leonard and Amy never shared any romantic subplot together, the two actors did recreate their childhood kiss on a late-night talk show while promoting The Big Bang Theory.

While Bialik and Galecki didn’t date outside of Blossom, Galecki and Penny’s actor, Kaley Cuoco, were romantically involved while making The Big Bang Theory. The pair dated while filming the series and amicably parted ways long before the show ended. However, they didn’t admit this until years after the fact despite a lot of scrutiny from the press. Apparently, the duo’s chemistry did translate into a real-life romance, but The Big Bang Theory stars’ relationship didn’t last.