This year brings with it the end of an era. No, not Avengers: Endgame nor Star Wars: Episode IX. Come May, The Big Bang Theory will air its final episode ever, bringing the screen antics of Leonard, Penny, Sheldon, and company to a close.

While twelve seasons and 268 episodes might not quite rank Big Bang as the longest running sitcom of all time, the Chuck Lorre and Bill Prady created series is up there. Over twenty million viewers watched the show at its peak in the US alone and its global fan base is huge.

For those who have spent the last twelve years under a rock, The Big Bang Theory is a CBS comedy about a group of scientists, and their aspiring actress friend, who live in Pasadena, revel in geek culture, and regularly get into hilarious misdemeanors. Each episode is excessively titled to resemble a pseudo-scientific principle and balances quick wit with genuine science.

Over the years, the cast has expanded from five to a ensemble of nine regulars, including Melissa Rauch’s Bernadette and Kevin Sussman’s Stuart, the hapless owner of the gang’s local comic book store. In the face of growing accusation that the show's become repetitive and tired, it's barreled on regardless.

References and Easter eggs, not to mention some mind-boggling star cameos, have littered the show from day one but, with so many to catch, it’s all too easy to regularly miss the best of them.

With this in mind, we’ve scoured the show’s back catalogue to search where no fan has searched before and found 29325 Little Things Fans Completely Missed In The Big Bang Theory.

24. Sheldon’s T-shirts Mirror His Emotions

Howard wears turtle necks, Raj favours a cardigan and Leonard likes his polos topped with an unbuttoned shirt. When it comes to clothing on The Big Bang Theory, consistency rules.

Sheldon, in this regard, is no different and can usually be found sporting a short-sleeved t-shirt over a long one with its sleeves rolled up.

There is, however, a fun theory that suggests the colors of Sheldon’s top layer tee is far from random. The theory states that Sheldon wears red when he’s angry, orange when he’s greedy, yellow when he’s afraid, blue when he’s hopeful, purple when he’s in love, indigo when being comionate, and green when his willpower is strong.

Whilst this doesn’t always work, it’s a very convincing theory in many an episode.

23. Amy’s Flat Number Was Math Famous 

Now that Amy and Sheldon live together, it’s easy to forget that not so long ago Amy had an apartment of her own. It was there that the pair kissed for the very first time – in ‘The Agreement Dissection’ – and there that Sheldon presented Amy with their first Relationship Agreement.

One little thing fans might not have noticed, however, is that Amy’s old apartment number was no coincidental digit. The number on Amy’s door qA 314, which are also the first three numbers in the mathematical constant ‘Pi’. The full number is 3.14592653589793238462643383279502... and so on

22. Penny’s Fridge Gives The Game Away

Most TV shows do their best to hide the fact that they’re not actually real – give or take the odd in-joke and reference – but there’s one Easter Egg in The Big Bang Theory that gave the game away for any fan prepared to look close enough.

Back when Penny lived across the hall in apartment 4B, she covered her fridge in photographs. It was a nice touch, but what you might not have realized is that in these photographs were  of the cast and crew of the show. Some of them moved with her to 4A too.

21. Sheldon’s Favorite Number

Sheldon really loves the number 73. While he didn’t explain his reasoning until the show’s seventy-third episode – ‘The Alien Parasite Hypothesis’ – the clues had been present for quite a long time. This was particularly clear in just how many t-shirts Sheldon owns with the number on it.

So, what’s so special about 73? In Sheldon’s own words: "73 is the 21st prime number. Its mirror, 37, is the 12th and its mirror, 21, is the product of multiplying 7 and 3”. In binary, 73 is a palindrome too and it’s also the year in which Jim Parsons was born! Neat, right?

20. Where'd  Your Voice Go, Bernadette? 

Melissa Rauch ed The Big Bang Theory back in the show’s third season. At that time, she worked at The Cheesecake Factory and was set up for a relationship with Howard by her colleague Penny. By the following season, Bernadette was a series regular and before long the two married.

One little thing fans may not have noticed, however, is that Bernadette’s voice wasn’t originally as high pitched as it is these days. As it transpires, Rauch was encouraged to change her voice when she became a regular to distinguish her with co-star Kaley Cuoco.

19. Penny’s Missing Something Important

What’s Penny’s last name? Wrack your brain and Google it as much as you like, but you won’t find the answer and for very good reason. In the show’s early days, it was just chance that no one ever mentioned Penny’s surname but, as the series ran on, the decision became more significant.

Executive producer Steve Molaro has put it down to superstition, suggesting that the root of the show’s success may well be down to their never having revealed Penny’s name. Since marrying Leonard at the close of season eight, however, Penny has become a Hofstadter.

18. A lot Happens In The Laundry Room

The Laundry Room has been a staple of The Big Bang Theory since the first season. Whilst most of the characters in the show – and the human race, as it goes – do their laundry as and when they need to, Sheldon does his at 8.15pm on Saturdays.

One little thing fans might not have noticed in the Laundry Room is the tiny note on the wall that suggests that Sheldon isn’t the only resident in the building with eccentric habits. The note – which wasn’t there in the room’s first appearance – reads: ‘Please keep your clothes on while doing laundry’. Interesting…

10. Amy Has Two Moms

Recent series of The Big Bang Theory have seen Kathy Bates the show as Amy’s mother with increasing regularity. As wonderful as Bates is in the dour role, one little thing fans of the show completely missed is that Mrs. Fowler was originally played by a completely different actor.

Amy’s mother first appeared in the show during its fourth season, where she was played by Annie O’Donnell. After just a handful of episodes, the character disappeared from the show until season ten – by which point Bates had taken over.

9. Leonard And Sheldon Are Tribute Names

Now well-known across the world, Leonard Hofstadter and Sheldon Cooper’s names were inspired by three key figures in the history of science and television. Robert Hofstadter was the winner of the 1961 Nobel Prize in Physics for his pioneering work in the field of electrons. Leon Cooper was a fellow Nobel Prize Laureate, known for discovering ‘the Cooper pair.’

The character’s first names, meanwhile, were created in honor of American film and television producer, director, writer, and actor Sheldon Leonard. In a quirky twist, Johnny Galecki was originally top choice for the role of Sheldon but felt he was better suited to Leonard.

8. The Props Got A Lot Geekier

From Doctor Who and The Flash to Star Trek and Batman, the characters in The Big Bang Theory love their film, television, and comic book memorabilia. As such, in any given episode of the show, it is usually possible to spot the odd posable action figure somewhere in the background.

What you may not realize, however, is that pop culture props weren’t always so prominent on the show. Sure, the first half of season one was full of references, but Leonard and Sheldon’s apartment was relatively sparse on Daleks and Norse hammers until 'The Nerdvana Annihilation'. Originally, the flatmates preferred scientific clutter.