Any show can make a meta-nod to another show or pop-culture property.
But it takes a very special programme to refer to its own history – it's usually a sure sign that a telly programme has reached icon status (or that its creators have become too big for their boots).
Here's some of our favourite meta reference moments.
1. The Walking Dead – 100th episode
The 100th episode of The Walking Dead may have been divisive, but there's one thing it was definitely good at: shoehorning in references to loads of previous episodes.
A lot of people noticed the season one nods, but there are references to basically the show's entire history scattered throughout.
You can see all of them in the video above.
Our favourite? Rick's quote about society relying on windows staying intact, which totally explains why the gang shot out all of the Saviours' windows (something that really confused us when it was happening, but now totally makes sense).
2. Frasier – 20 years
In season eleven's 'Caught In The Act' Frasier's ex-wife, children's entertainer Nanny G, asks him "Do you have any idea what it's like playing the same character for twenty years?"
Of course, Kelsey Grammer knew exactly what that was like – he'd played Frasier since 1984.
The gag gets a big laugh from the studio audience, and Grammer milks it for all its worth with some expert mugging.
3. The X-Files – Hello Clarice
In 'Never Again', Jodie Foster voices a tattoo (don't ask) that randomly hates Scully.
Scully was originally based on Clarice Starling, a character played in the Silence of the Lambs by Jodie Foster, so it's logical that Foster would be annoyed by a character who's technically a rip-off of one she made iconic. It's a fairly deep-cut reference, which only true long-term X-geeks would get.
So, it makes sense that the episode was originally meant to be directed by Quentin Tarantino (until Director's Guild rules prevented him from doing so).
4. Rocky and Bullwinkle – network notes
This one's mainly amazing because it should have been career suicide for the writers. After receiving an official warning about a previous episode's references to cannibalism, the Rocky and Bullwinkle team wrote a joke into the next episode about Rocky using the actual network complaint to get out of being eaten.
It's an early example of the sort of network-baiting meta-gag that Family Guy would eventually own.
5. Seinfeld – the show about nothing
Season 4 of Seinfeld is a major fan favourite, mostly because it deconstructs the show completely.
When Jerry Seinfeld's character is asked by NBC executives to pitch an idea for a TV series, Jerry and George come up with an idea for a "show about nothing".
The plotline mirrors exactly Jerry's experiences with Larry David (who George is closely based on) conceiving and pitching the show, brilliantly plundering the past to create a compelling season-long arc.
6. Curb Your Enthusiasm – the reunion
Speaking of Seinfeld, Curb Your Enthusiasm, which follows the real-life Larry David (frequently introduced to new people on the show as the co-creator of Seinfeld, mainly because he is) took meta to the next level when he brought Seinfeld into the Curb Your Enthusiasm timeline to reunite the cast for a reunion episode, to give his estranged wife Cheryl a part on the show.
So, Larry's referring to his own past career, and, in the video above, we see him trying to play George (a Seinfeld character who's based on him) in Curb (a show where he plays a character with his own name). Oh, and Larry David's not very good at playing George, despite the fact he's brilliant at playing 'Larry David'. Our brains might explode in a minute.
