"Kurisumasu ni wa Kentakkii" - or "Kentucky for Christmas", is the habit of eating Kentucky Fried Chicken (KFC) on 24 December.

It began as an inspired bit of marketing in the 1970s, when KFC noticed that expatriates who craved Christmas turkey turned to fried chicken as the closest available substitute. Now a popular Japanese tradition, customers queue around the block, and some pre-order their meal as early as October.

Christmas, of course, is not a religious holiday in Japan, where a tiny minority of the population is Christian.

But "Kurisumasu ni wa Kentakkii" demonstrates how easily commercial interests can hijack religious festivals - from Diwali in India to Passover in Israel, but most notoriously, Christmas in America.

Why, after all, does Santa Claus wear red and white?

Many people will tell you that the modern Santa is dressed to match the red-and-white colours of a can of Coke, and was popularised by Coca Cola's advertising in the 1930s.

A good story, but the red-and-white Santa himself wasn't created to advertise Coca-Cola - why, he was touting the rival beverage White Rock back in 1923.

Rudolph the Red-Nosed Reindeer was the one who was invented as a marketing gimmick.

The modern Santa Claus is actually much older, a patchwork character woven together from different sources.

These include Saint Nicholas, a 4th Century Greek bishop - who famously wore red robes while giving gifts to the poor, especially children - and the English folk figure "Father Christmas", whose original green robes turned red over time.

The Santa we know also owes much to the Dutch figure Sinterklaas - also based on Saint Nicholas - whose legend flourished in the once-Dutch city of New York, popular with prosperous Manhattanites such as Washington Irving and Clement Clarke Moore in the early 1800s.

Mr Irving and Mr Moore also wanted to turn Christmas Eve from a raucous partying of street gangs into a hushed family affair, everyone tucked up in bed and not a creature stirring - not even a mouse.

Mr Moore - who penned the line "'Twas The Night Before Christmas" in 1823 - did as much as anyone to create the American idea of Santa Claus, the red-robed patron saint of giving presents to everyone whether they want them or not.

It was in the 1820s, too, that advertisements for Christmas presents became common in the United States. By the 1840s, Santa himself was a frequent commercial icon in advertisements. Retailers, after all, had to find some way to clear their end-of-year stock.

The gift-giving tradition took firm hold.

In Boston in 1867, 10,000 people paid to see Charles Dickens give readings of his Christmas Carol - a story light on biblical details and heavy on the idea of generosity.

Down the coast in New York the same year, Macy's department store decided it was worth keeping the doors open until midnight on Christmas Eve, for last-minute Christmas shoppers.

The next year, Louisa May Alcott's novel Little Women was published. Its first line: "Christmas won't be Christmas without any presents."

The Christmas blowout, then, is not new.

Prof Joel Waldfogel, an economist and author of Scroogenomics, has been able to track the impact of Santa on the US economy back across the decades.

By comparing retail sales in December with sales in November and January, Prof Waldfogel has estimated the size of the Christmas spending bump all the way back to 1935, the era of the Coca-Cola Santa.

In fact, relative to the size of the economy, Christmas spending was three times bigger then than now. What is an everyday indulgence today would have been a once-a-year treat back in the 1930s.

Prof Waldfogel has also compared the US Christmas boom to other high-income countries around the world. Again, perhaps surprisingly, the US's December spending boom is not particularly large, relative to other countries.

Portugal, Italy, South Africa, Mexico and the United Kingdom have the largest Christmas retail boom relative to the size of their economies; the US is an also-ran

Source：BBC