- Casting Gag:
- In the episode "Last Gasp", one character mistakenly refers to a girl called Tamsin as "Jasmine". He is immediately reprimanded for the mistake by a character played by Tamsin Greig.
- A casting coincidence rather than a gag, but the silent comedy episode "A Quiet Night In" features actress Oona Chaplin, granddaughter of Charlie Chaplin.
- The location used in "The Trial of Elizabeth Gadge" was used in Horrible Histories, and features Jim Howick, notable regular on the show. Shearsmith and Pemberton also made appearances in the late seasons of Horrible Histories as Hollywood agents alongside Mark Gatiss.
- It's mentioned in "The Understudy" that Michele Dotrice once starred opposite Tony in Richard III. Dotrice was later cast as Marion in "The Twelve Days of Christine."
- Directed by Cast Member: Pemberton and Shearsmith co-directed 'Cold Comfort' and 'Nana's Party'.
- Production Posse: Steve Pemberton starred alongside Elsie Kelly (Nana in "Nana's Party") in the ITV sitcom Benidorm for several years, and David Warner (Justice Pike in "The Trial Of Elizabeth Gadge") appeared in the film adaptation of The League of Gentlemen in scenes set in a similar time period as 'The Trial Of Elizabeth Gadge'. Vilma Hollingberry, the voice of the elderly caller in "Cold Comfort", had a recurring role in Psychoville opposite Pemberton and Shearsmith.
- Promoted Fanboy: Jack Whitehall (Hugo in 'La Couchette') was a fan of Series 1 and asked Shearsmith and Pemberton if they could find "a Jack Whitehall-sized hole" in Series 2.
- Similarly, Alexandra Roach (Nina in 'The Riddle of the Sphinx') was a big fan of the first two series.
- Take That!: The creators have stated that a character in "Speaking Out Loud" is based on a social media influencer whose behaviour they considered selfish.
- What Could Have Been: In an interview with the BBC's Writer's Room website, Pemberton revealed that an earlier version of Series 1's "The Understudy" would have featured David and Maureen Sowerbutts with Maureen as a Lady Macbeth-type character persuading David to murder his co-stars and secure a bigger role. It was later decided that "ultimately though it didn't feel right to mix up the worlds like that, and Inside No. 9 had to earn its own place in the comedy universe without leaning on our past work." David and Maureen did eventually appear in Series 5's "Death Not Be Proud", although in a very different story to the idea shown above.
- While writing 'La Couchette', Shearsmith and Pemberton considered playing Les and Maxwell, respectively. Pemberton also considered playing Les before deciding on Jorg.
- The Devil of Christmas was supposed to be a straight story about the The Krampus; but Shearsmith and Pemberton re-wrote the script after discovering there is a recently released horror movie about Krampus.
- At a preview screening of Season 3 the creators claimed that when writing "The Bill" they found it difficult to decide whether Philip Glenister's character should be an Upper-Class Twit or a brash nouveau-riche type, and alternated between the two in different drafts of the script (eventually settling on the latter.)
Trivia / Inside No. 9