Each year the book world seems to throw up yet another wildly unexpected bestseller, the kind of title publishers hope might become a January novelty, but which goes on to outsell everything in its wake.
But how on earth, in an era when bestsellers tend to be heavily advertised cookbooks or else vampiric sagas, does it happen?
Previous holders of this seasonal accolade have included Ben Schott's Schott's Miscellany, a clever compendium of what Stephen Fry described as "essential trivia" (and which spawned several sequels), and Lynne Truss' witty plea for grammatical adherence, Eats, Shoots & Leaves. The latter sold in millions around the world.
This year's proud recipient is Mark Forsyth and his delightful book The Etymologicon: A Circular Stroll Through the Hidden Connections of the English Language. Like those bestselling predecessors, it's essentially a book for viewers of QI, witty and erudite and stuffed with the kind of arcane information that nobody strictly needs to know, but a pleasure to learn nonetheless.
An example: Farts, he writes, are quickly delivered and slowly forgotten. Any accompanying smell quickly peters out, but did you know that the French word for fart is peter, and that from peter comes petard, which means a little explosive?
The book is, by the author's own admission, "absolutely a defecatory volume."
Forsyth, a 34-year-old Oxford graduate and now journalist, became convinced that he was not alone in his love of the origin of words, and in 2009 started a blog about them, The Inky Fool. The site quickly began amassing 4,000 hits a week, and came to the attention of Icon Books, a small, independent publisher, who took a punt on it. They published in November.
The Etymologicon swiftly picked up positive early press, not just in the broadsheets but also the nation's leading tabloid.
"That was a particular moment of victory," Forsyth says, smiling.
"I'd written a book that mentions De Quincey and John Dalton, and I end up with a half-page spread in The Sun."
Advanced publicity, and good reviews, sustained decent, if ultimately modest, sales: "The most sober expectation I had was that it might make it into the top 100," Forsyth says.
By mid-December, it had seemingly had its moment, peaking at a respectable 250 on Amazon's bestseller list. But then, in late December, windfall: Radio 4 made it Book of the Week. Within an hour of transmission, it had risen 100 places, and by that evening, to No 12. Forsyth was pinching himself.
"I spent the entire Christmas period constantly clicking "refresh" on Amazon, and watching it climb even higher," he recounts, still incredulous.
Three days before Christmas, this little book that looks at the origins of the word testicles and examines why Thomas Crapper's surname has become slang for number twos, reached No 1. Almost a month on, it's still in the top five, now a bona fide word-of-mouth sensation. The more it sells, the more it sells – at last count a full 50,000 copies.
Small fry compared to Jamie Oliver perhaps, admits Icon MD Philip Cotterell, but significant for an independent publishing house.
"Nobody knows what the winning formula of an unexpected bestseller is," Cotterell says, "and so we can only ever rely on instinct and judgement, belief and luck."
The publisher is understandably overjoyed, not merely at his author's success, but what it also suggests about the reading public in general.
"It goes to show that people still want to buy books that are well produced and possess a certain amount of imagination," he says.