It is about a boy (Finbarr) who is always listening in on conversations (often between his divorced mother and their neighbour, Mr. Gimlet, who she constantly ends up having sex with) involving very suggestive and often sexual double entendres. Often he does nothing but sit and laugh, making noises such as "Fnarr! Fnarr!", "Warf! Warf!" and "K-Woo! K-Woo!"
When talking of his wife's antique camera, a man says "I've spent many a hot afternoon with my face under her hood, flicking away at that button, trying to make those leathery old flaps to open up."
When talking of his picture printing apparatus he says "I've got a small Johnson, but it can enlarge to nigh on a foot when it is turned on a darkened room"
When demonstrating how easy it is to take off the lens he says "A few quick twists of the wrist and it comes off in a couple of seconds... Mind you I haven't had it off in ages, so it was very stiff this morning"
When talking about taking pictures of people he passes on the street, he says "I often startle passers-by when I suddenly pull it out of my trousers and it goes off in their eyes."
When describing the lamp in his darkroom he says "Mine's quite large and glows red at the top"
He is sometimes vistied by his mother's Russian friend, Sergei. Unfortunately, Sergei's English is very bad, which results in his sentences being corrupted in often lewd ways (for instance, "Your mother wants me to fetch her aerosol" becomes "Your mother wants me to felch her arsehole).
Typically the final frame of the cartoon features mother and friend going off to perform a sexual act. They even say what they are up to but this time Finbarr fails to laugh and comes up with an innocent explanation which he shares with the reader.
For example, an aspiring comedian may, when ordering a drink at a bar, say "Mine's a large one." The innocent meaning is that his usual drink is served in a large measure, while the hidden meaning implies that he has a large penis.
There is a cartoon strip in the English comic book Viz entitled FinbarrSaunders and his Double Entendres, about a youngster who enjoys this form of joke.
When Finbarr detects a double entendre, the cartoonist renders his sniggers as "Fnarr fnarr!", a usage that has entered English slang.