11 Best Big Bang Theory References You Missed In Young Sheldon

Sheldon Cooper from "The Big Bang Theory" is a quirky character whose idiosyncrasies have endeared him to audiences for more than a decade. On "The Big Bang Theory," his antics made some wonder what the eccentric Sheldon must have been like as a child and how his mother managed to raise him by herself. 

"I'm not crazy, my mother had me tested," is just one tantalizing Sheldon bon mot that seemed to indicate as much humor in the character's past as in his present. his was augmented by frequent mentions of his upbringing in Texas, his now-deceased father, his overly religious mother, and two siblings.

Jim Parson's portrayal of the character garnered him four Emmy Awards, but it made a lot of sense to "Big Bang" loyalists when the prequel/spinoff "Young Sheldon" was devised in 2016 (from an original pitch by Parsons, who serves as an executive producer on the show). Debuting in 2017, the series is now well north of 100 episodes, chronicling the early life of the character (now played by Iain Armitage) in Texas, beginning at age 9 in 1989. 

Alongside family members including his mother Mary (Zoe Perry), father George (Lance Barber), brother Georgie (Montana Jordan), twin-sister Missy (Raegan Revord), and his beloved grandmother Connie (Annie Potts), the show is as entertaining as it is heartwarming. Much like the hints of Sheldon's past in "The Big Bang Theory," the prequel has returned the favor, peppering in throwbacks and references to its parent show, often cleverly buried within its narrative. Below are some of the best "Big Bang" references you may have missed in "Young Sheldon."

In "Big Bang" canon, a man named Arthur Jeffries was the host of a children's science show called "Professor Proton," and it inspired Sheldon to pursue a career in science at a young age. But in the ensuing years, Jeffries became downtrodden, with his wife leaving him for the puppeteer on his show; ultimately, he became a reluctant party entertainer. 

Introduced in Season 6, Episode 22 of "The Big Bang Theory," Jeffries was played by legendary comedian Bob Newhart; the role earned the comedy veteran an Emmy for outstanding guest actor in a comedy series, and with repeated appearances the "Newhart" and "Bob Newhart Show" legend became a fan favorite.

Although he is now into his nineties, Newhart is still making people smile. Newhart appeared in a blink-and-you'll-miss-it cameo in the pilot episode of "Young Sheldon" via the Professor Proton show, watched by young Sheldon and clearly having an inspiring effect on him. The character would go on to make two more cameo appearances through the Cooper family's television set in the first two seasons; more recently, Professor Proton references have been strictly verbal, but another cameo from one of television's all-time legends certainly doesn't seem outside the realm of possibility.

Jim Parsons, Mayim Bialik, and Simon Helberg aren't the only ones from "Big Bang" to have their voices featured on "Young Sheldon." Kaley Cuoco made a voice cameo appearance in a Season 3 episode of the prequel show that might be tricky to spot, since Cuoco isn't voicing her "Big Bang" character Penny and her name doesn't appear in the end credits. 

In "Teenager Soup and a Little Ball of Fib" (Season 3 Episode 10 ), Sheldon is faced with having to attend a swim test at his school. Dreading the bacteria that rests in the school's swimming pool, germaphobic Sheldon does everything in his power to avoid it, including faking an illness to avoid going to school altogether. His guilt induces a nightmare where the pool water (voiced by Cuoco) entices Sheldon to come closer by promising that it's clean and hygienic, only to gobble him up, waking a startled Sheldon. Cuoco's presence — and her dynamic with Sheldon — is reminiscent of a running gag in "Big Bang" where Penny would often frighten the neat-freak Sheldon with her messiness.

Adding to the plethora of ways "Big Bang" is a lot like "Friends," there's a song that gives Lisa Kudrow's "Smelly Cat" song a run for its money: The similarly-feline-themed "Soft Kitty" lullaby in "The Big Bang Theory." 

In "Big Bang," Sheldon would often insist whomever was taking care of him (mostly Penny) to sing the song whenever he would be sick or sleepy, as he claimed his mother did during his childhood. This running gag yielded several memorable moments on the series, like the time Penny asked Sheldon to sing to her when she was injured and under medication, or when Sheldon sang it to a dying Professor Proton in the hospital.

Since Sheldon made repeated mention of his mother Mary singing the song to him throughout his childhood, it makes sense that it appears frequently in "Young Sheldon," making its first appearance in "A Sneeze, Detention, and Sissy Spacek" (Season 1 Episode 13). At the end of the episode, Mary sings "Soft Kitty" to Sheldon on his bed when he has the flu, tying back to a memorable "Big Bang" moment with Sheldon (slightly) more grown up.

Keeping mental notes of one's grudges can be both tiresome and draining — especially for Sheldon Cooper, who would prefer to preserve his mental energy for more important pursuits in life such as science, physics, and countless hours of gaming, comic-book reading and rewatching old episodes of "Star Trek." Sheldon's solution? A list of his "mortal enemies," kept on a five-and-a-quarter-inch floppy disk. 

Noteworthy individuals unfortunate enough to be included on the list include Wil Wheaton (although he has been removed from the list on two separate occasions) and Joel Schumacher, for "nearly destroying the Batman franchise."

The presence of the floppy disk and a few other clues have always seemed to imply that Sheldon has been maintaining this list since the late 1980s/early 1990s — essentially, his childhood. This was confirmed in the "Young Sheldon" episode "A Computer, a Plastic Pony, and a Case of Beer" (Season 1 Episode 22), which had Sheldon falling in love with a computer he spots at a local Radio Shack, particularly for its ability to "easily alphabetize" his list of enemies and their transgressions. As the title partly suggests, the computer would become a focal point for the episode, with Sheldon unwittingly sparking a heated disagreement between his parents about their finances after asking them to buy him the computer.

In "The Big Bang Theory," Sheldon's mother Mary Cooper is firmly established to be, in Sheldon's words, a "kind, loving, religiously fanatical right-wing Texan with a mild Dr. Pepper addiction." Apart from said addiction, Sheldon additionally revealed in a sleepy stupor (Season 2, Episode 1: "The Bad Fish Paradigm"), that his mother had a secret (and rather nasty) smoking habit during his childhood in. "Mom smokes in the car," he explained. "Jesus is okay with it, but we can't tell Dad."

Sure enough, "Young Sheldon" has Mary secretly reaching for a cigarette whenever she's tense, also depicting a woman who was once a rebellious teen, much like Georgie is now. The first instance of Mary smoking was shown in "A Secret Letter and a Lowly Disc of Processed Meat" (Season 3 Episode 21), brought on when Mary got distressed by the possibility of 11-year-old Sheldon leaving the nest after getting an offer letter from CalTech. Then, in "A Lock-In, a Weather Girl and a Disgusting Habit" (Season 5, Episode 11), as marital problems threaten George and Mary, George comes home to patch things up with his wife, only to find her bonding with Pastor Rob over a smoke.