The Green Clarinet forces you to reveal a shameful secret... to the tune of "I Saw Three Ships".
Genius Bonus: One The Quiz Broadcast sketch has the Test Card Girl writing "Revelation 6 13 15" on the blackboard.
Revelation 6:13-15 reads: "and the stars in the sky fell to earth, as late figs drop from a fig tree when shaken by a strong wind. The sky receded like a scroll, rolling up, and every mountain and island was removed from its place.
Then the kings of the earth, the princes, the generals, the rich, the mighty, and every slave and every free man hid in caves and among the rocks of the mountains."
Also, during the Cheesoid sketch, about an expert soup chef who loses his sense of smell. The chef has his copy of Perfume stolen, a book about a character with an overwhelming obsession with the sense of smell.
One of the Didldidi supermarket ads says that some of the bargains were due to stock having to be sold off before changes to the Trade Descriptions Act came into force. It sounds like they're making up an excuse for Rule of Funny, but the Trade Descriptions Act really was completely overhauled around that time.
Harsher in Hindsight: Angel Summoner and BMX Bandit, about a duo of superheroes with vastly different power levels and the tension this creates, is a rather apt metaphor for Mitchell (Angel Summoner) and Webb's (BMX Bandit) later careers.
BMX Bandit: Your ability summon a horde of celestial superbeings at will is making my BMX skills a bit...redundant.
The Orphaned Punchline about Jimmy Savile receiving three life sentences. "You think you know a guy, and then he does something like that..." Although, considering that it was allegedly an open secret at the BBC, it may simply have been a deliberate (if slightly sick) In-Joke that "got out".
"The Quiz Show"'s Running Gag of post-apocalyptic survivors trying at all costs to avoid remembering "the event" becomes downright hilarious in the wake of the failed American sci-fi drama The Event, which had a marketing campaign that revolved entirely around obfuscating what the titular event is, and was also a massive disaster.
The villain in the Casino Royale (2006) spoof doesn't look much like Le Chiffre, but he does resemble later Bond villain Silva.
In the radio version, Olivia Colman plays Queen Elizabeth II in a sketch involving the Queen getting ridiculously excited over a bunch of D-grade acts being contracted to play the Royal Variety Performance. In 2017, it was announced that the role of Elizabeth II in seasons three and four of The Crown (2016) was going to be played by... Olivia Colman.
Retroactive Recognition: In the Numberwang sketches, most viewers will recognise Simon as Paterson Joseph, who's best known for his portrayal as Alan Johnson in Peep Show. Funnily enough, the show also stars David Mitchell, Robert Webb and Olivia Colman.
Seasonal Rot: Many fans will either believe that Series 3 or 4 was when the humour wasn't as good as the previous series.
The Woobie: A number of the characters, but possibly Cheesoid is the biggest one. Created to identify smells, it ends up just barely being able to identify cheese and petrol, frequently getting them mixed up and even mispronouncing "petrol" as "petril."
"Cheesoid kill self. Cheesoid kill self with petril. Why petril not burn?"
"No Cheesoid, that's not petrol!"
"PetROL! That's cheese!"
"Hate self. Why Cheesoid exist? Cheesoid so lonely..."
YMMVs for That Mitchell and Webb Situation:
Ending Fatigue: A one-episode recurring gag where Mitchell and Webb play co-workers in various professions who end every scene with a quick kiss.