As more people enter the room and step into the wardrobe, secrets shared by some of the characters are revealed, with various allusions to incestuous relationships, child abuse, and adultery.

In addition to the writers, the episode starred Katherine Parkinson, Tim Key, Luke Pasqualino, Ophelia Lovibond, Anne Reid, Julian Rhind-Tutt, Anna Chancellor, Marc Wootton, Ben Willbond and Timothy West.

The cast and writing were praised by television critics, and the episode was chosen as pick of the day in a number of publications.

The comedy writers and actors Steve Pemberton and Reece Shearsmith, who had worked together on The League of Gentlemen and Psychoville, took inspiration for Inside No.

9 was a "reaction" to Psychoville, with Shearsmith saying that "We'd been so involved with labyrinthine over-arching, we thought it would be nice to do six different stories with a complete new house of people each week.

"[4] The format of the series pays homage to Tales of the Unexpected, The Twilight Zone and Alfred Hitchcock Presents.

[2] In addition to Pemberton and Shearsmith, "Sardines" starred Katherine Parkinson, Tim Key, Luke Pasqualino, Ophelia Lovibond, Anne Reid, Julian Rhind-Tutt, Anna Chancellor, Marc Wootton, Ben Willbond, and Timothy West.

[3] Pemberton described the concept of "Sardines" as "a simple idea" and he was happy that they did not "have to worry about the consequences of it", due to the format of the series.

[6] "Sardines" was written so that a feeling of claustrophobia would develop as the story progressed; Pemberton said that "our first consideration was, 'Can we get 12 people in a wardrobe?'

[6] Writers for Broadcast described seeing the assortment of actors "crammed inside an imposing wardrobe" during filming as "an arresting spectacle".

For the director David Kerr, the difficulty was sustaining the illusion that everything was happening in one place, ideally without viewers realising that there was a technical challenge involved.

He aimed to avoid "leading" the audience with regard to the more important characters by "not giving [them] coverage" earlier in the episode.

As the group talk, Mark (Jeremy's boss) and his wife, Liz, enter the bedroom, unaware of the people in the wardrobe.

Jeremy enters and tells Rebecca he is going to pick up another guest from the train station, but as he turns to leave he mistakenly calls her "Rachel".

[18] For Ryan Lambie, writing for the entertainment website Den of Geek, the single-camera setup and Kerr's direction gave the episode "the tense look of an early Hitchcock film, all low angles and illuminating shafts of light".

Tropes of Britishness identified by the critic David Upton include the dated clothing and the awkward interaction between Rebecca and Ian at the start of the episode.

[9] With the introduction of the noticeably younger Lee, there is a clash of customs, illustrating the differing norms of the respective generations.

[18] This "1940s aesthetic" and the fact the story took place in a single location tied the episode to "a golden age of plays on British television".

[2] Writing in The Daily Telegraph, Paul Kendall identified some of Shearsmith and Pemberton's "regular tropes" utilised in the episode; namely "a bunch of misfits, uncomfortable silences and allusions to dark crimes in the distant past".

[17] Particular themes addressed in the episode include murder, incestuous relationships, child sexual abuse, vengeance and adultery.

[2][20] As the episode progresses, secrets related to these themes are revealed to be the explanation for apparently innocuous tendencies, such as Carl's dislike for the sardine song and John's aversion to soap.

[28] Harry Venning, writing for The Stage, described the cast as "impressively stellar", and also commended the writers' performances.

[20] The comedy critic Bruce Dessau said that the "cast alone is almost recommendation enough",[21] while another reviewer said that if "a bomb dropped on the cupboard where they were hiding, a good portion of the acting talent in this country would be wiped out.

Journalists also lauded the script, with Kendall labelling the dialogue "perfectly pitched",[16] Dessau calling it "tightly written" and without wastage,[21] and Owen praising the way each character was "delivered into the story at the exact right moment".

[8] Brad Newsome, writing for The Sydney Morning Herald (the episode having been shown in Australia on BBC First in 2015), said that the episode was "deftly written",[29] and Venning said the "lean, mean narrative didn't just twist and turn, it folded back upon itself to provide a totally unexpected, profoundly disturbing and deeply satisfying denouement".

[20] On The Arts Desk, Lee praised the direction of Kerr, saying that he delivered "a pitch-perfect piece with no character overwritten or line overplayed".

[17] A separate review in The Times, however, praised the twist ending; "this isn't just an inspired set-up performed by a stellar cast – it builds to a macabre and horribly imagined climax".

[8] Mark Jones, writing in The Guardian, gave a more mixed review overall, describing "Sardines" as a "slow burner, but a decent introduction to a series".