For twelve years, and nearly 300 episodes, The Big Bang Theory was one of the most popular shows in the world and one of the most beloved and successful sitcoms of all time. With its run now at an end, all that remains of the beloved series is its spinoff, Young Sheldon, which has aired two full seasons as of May 2019. Following the childhood and adolescence of one of Big Bang's main characters, Dr. Sheldon Cooper, Young Sheldon is basically The Wonder Years meets The Big Bang Theory—a fluffy slice of nineties nostalgia with just the right amount of nerd content.
Since Young Sheldon is providing the backstory for one of Big Bang's most important and most influential characters, it's inevitable that the series will refer to the original series on many occasion. Most of the series' main characters—including Mary Cooper, Missy Cooper, Georgie Cooper, and Connie "Meemaw" Tucker—have appeared on The Big Bang Theory over the course of the series. But other references have been might have been easy to miss. We recap ten of the best of them here.
10 The Origin of Bazinga
The Big Bang Theory's Sheldon Cooper has plenty of quotable lines, and even quite a few catchphrases, too. Arguably one of his most well-known and most-used catchphrases is the simple word "Bazinga!" whenever he finds something funny. As much as he used it throughout the series, The Big Bang Theory never explained exactly what "bazinga" meant, or where it came from. Thankfully, Young Sheldon resolved that mystery.
In the tenth episode of the second season, "A Stunted Childhood and a Can of Fancy Mixed Nuts," little Sheldon Cooper sets out to try and behave more like his age group out of fear that he may grow up to be an emotionally stunted adult. As part of his adventures in childish behavior, Sheldon visits a joke shop and learns about a line of prank products called Bazinga. The tagline for the products? "If it's funny, it's a Bazinga!" And thus a catchphrase was born.
9 "He's Blossom's brother."
Sheldon and his twin sister, Missy, couldn't be more different. Longtime fans of The Big Bang Theory universe could already tell that before Young Sheldon premiered, given Missy's brief appearance near the very beginning of the series. But Young Sheldon has only further highlighted the extreme differences between these siblings, with Sheldon as an academic wunderkind and Missy as a pop culture obsessed airhead.
"A Race of Superhumans and a Letter to Alf," the second season's eleventh episode, features a scene in which Missy is trying to come up with possible fantasy boyfriends for her Cabbage Patch doll, Celeste. One of her suggestions is Joey Lawrence, "Blossom's brother." Of course, Blossom starred none other than Mayim Bialik, who would go on to become Big Bang's Amy Farrah Fowler.
8 Mary Singing Sheldon "Soft Kitty"
Sheldon Cooper is a raging germophobe and unabashed about it. He's also very particular about his routines to begin with, and when he comes in the slightest bit of contact with germs, he becomes even more set in his ways and difficult to deal with. All throughout The Big Bang Theory, any time that Sheldon is remotely sick, he requires someone to sing him the lullaby "Soft Kitty," whether it's his mother Mary, best friend Penny, or eventual wife Amy who gets to do the singing.
"A Sneeze, Detention, and Sissy Spacek," the first season's thirteenth episode, introduces Sheldon's hyper fixation on remaining healthy in the presence of germs. Of course, the episode ultimately ends with Sheldon contracting the cold that's been making the rounds. But it also ends with a truly beautiful, heartwarming scene of young Mary Cooper serenading a sleepy, sick Sheldon with his beloved "Soft Kitty."
7 Young Amy is Reading Little House on the Prairie
Airing the same night as The Big Bang Theory's highly watched and much-lauded series finale, the second season finale of Young Sheldon, "A Swedish Science Thing and the Equation for Toast," included a touching, one of a kind tribute to the long-running series. After no one showed up for his Nobel Prize themed party, Sheldon was very upset and wondered whether he would be alone always. He ultimately came to the realization that he wouldn't, much like the quarks of science he understands so well.
But Young Sheldon offered a moving further exploration of this fact, including a montage of glimpses of all of Sheldon's eventual friends and loved ones during their own childhoods. One of those such glimpses showed a young Amy Farrah Fowler reading what we know to be Amy's most beloved book, Little House on the Prairie by Laura Ingalls Wilder.
6 Vernee Watson's Recurring Roles
It was fairly common for older sitcoms to feature the same guest actors in different roles. As sitcoms have moved toward more continuous storytelling, however, that trend has sadly gone the way of the past. But The Big Bang Theory and Young Sheldon universe offer a glimpse of this adorable little quirk of casting when it comes to the legendary television and stage actress Vernee Watson.
On The Big Bang Theory, Watson appears in a few episodes as Althea Davis, a no-nonsense nurse forced to deal with the guys in some of their more bizarre adventures. Johnson also appears on Young Sheldon in two episodes as a similar character, Nurse Robinson, who encounters the Cooper family in the 1990s Texas setting.
5 Sheldon Isn't Crazy, His Mother Had Him Tested
Yet another one of Sheldon's most memorable and highly quoted scenes from The Big Bang Theory finds him proudly declaring, "I'm not insane. My mother had me tested." Sheldon's behaviors are often maddening and inexplicable to those around him, even those who have known him for years, so it's an explanation trotted out quite often by both the series and the fans themselves.
Young Sheldon continues this trend by establishing Sheldon's sanity test as something that's already happened prior to the series. In the second season, Sheldon confronts a teenage boy who has been interfering with Georgie's love life and tries to arrange for a reconciliation. When Georgie asks him if he's crazy for doing that, Sheldon once again proudly states, "Nope, Mom had me tested!"
4 Sheldon's Signed Photo of Professor Proton
In the sixth season of The Big Bang Theory, the series finally introduces one of Sheldon's major childhood heroes: the television scientist Professor Proton, played by the legendary comic talent Bob Newhart, and clearly inspired by the beloved children's television host Bill Nye the Science Guy. When first meeting Professor Proton, Sheldon refers to a framed, signed photo of Professor Proton that he received during his childhood after writing the television star a fan letter.
Young Sheldon establishes perfect continuity with this, featuring that same framed and autographed photo on the wall of Sheldon's bedroom, right above his desk. He's also frequently watching Professor Proton's television show during multiple episodes, further emphasizing the role both the man and the series played in his young adult life.
Young Sheldon is a show with a lot of heart, but the series is always at its best and the most heartwarming whenever it focuses on the relationship between Sheldon and his grandmother, Meemaw. In The Big Bang Theory, it took until the series' ninth season for Meemaw to finally appear, but she was often discussed in many, many loving moments by her beloved little Moonpie, Sheldon.
The origin of the Moonpie nickname is explained by Sheldon in the second season episode "The Terminator Decoupling." "She calls me Moonpie because I'm nummy nummy and she could just eat me up," Sheldon bashfully tells Penny. Thankfully, Young Sheldon has picked up right where The Big Bang Theory left off, with Meemaw adorably referring to Sheldon by the sweet treat inspired nickname many times.
2 Young Leonard's Robe
We've already talked about the heartwarming montage that Young Sheldon included at the end of its second season finale. The first of Sheldon's eventual best friends that the montage includes is a then pint-sized Leonard Hofstadter, who is staying up late listening to the radio. Various items are scattered across his desk, including an inhaler, a toy robot, and some science notes.
But the clearest visual reference to the original series comes in the form of what Leonard is wearing: a cozy reddish brown-striped robe that is exactly the same pattern as the well-worn robe Leonard wears for the entire run of The Big Bang Theory. Clearly, it's not the same robe, but it shows that Sheldon isn't the only one with very particular tastes.
1 Relationship Agreements
Sheldon Cooper is nothing if not a pragmatic, fact-driven individual. Emotions are foreign territory to him, and he relies upon black and white definitions and outlines in order to understand what is required of him in certain relationships. In The Big Bang Theory, he has a roommate agreement with longtime roommate Leonard, and eventually a relationship agreement with girlfriend turned wife Amy Farrah Fowler.
But the first of these agreements that Sheldon ever drafted wasn't for any of his own relationships, but rather for the budding romance between his Meemaw and his mentor, Dr. John Sturgis. Sheldon drafts this contract for the couple in Young Sheldon's first season finale, "Vanilla Ice Cream, Gentleman Callers, and a Dinette Set," and Dr. Sturgis even serves as Sheldon's first ever notary.