"What are you doing?" I asked.
"Trying to earn some money," he replied, matter-of-factly. "I need it to get a Bin Weevil membership."
"But what's with the tooth?"
He looked at me in that Durr-Are-You-Completely-Thick-Or-What? way that children have before explaining: 'Alex at school gets £5 from the tooth fairy for every tooth. I've counted my teeth and if I lose them all I can get a year's membership.'
Now, dear reader, what in the above sentence sticks out like a sore thumb to you?
Yes indeed. £5. FIVE WHOLE POUNDS. For a tooth. I'm thinking about getting in the boxing ring with both Klitschko brothers and asking them to punch this month's mortgage payment out of my mouth.
When on earth did the loss of a milk tooth turn into a mini-industry: Tooth Fairy Inc?
I was shocked by my son's revelation, but I did buckle to pester power and agreed to "have a word with Ben Elf (the name of the fairy that visits our boys)" to see if he would increase his dental recovery contribution from 50p to £1 per tooth.
"Aww, but Da-ad, that'll take me five whole teeth to get a Bin Weevil membership – for just one month," he protested.
"Then, son," I replied. "You'd better get some stronger cotton."
Before this exchange, I naively believed there was a universally agreed price per tooth, laid down by the Pillow-Lifting Sub-Committee of the Grand Council of Tooth Fairies.
When I was growing up, we'd get a sixpence per tooth and so, allowing for inflation, I've always thought 50p was in keeping with T.F.E.P. (Tooth Fairy Economic Policy).
But no, much as the price of bread and beer varies from region to region in the UK, so too does the cost per tooth.
Discount website www.MyVoucherCodes.co.uk surveyed 2,091 parents of children aged between four and 12 and found that the tooth fairy is more generous in some parts of Britain than others.
In London, where the fairies fly around with personal bodyguards to protect their gold-plated wings, children receive AN AVERAGE of £5.10 per tooth. That's £100 for a full set of milk teeth. No wonder the children of capital-based oligarchs and celebrities just keep getting richer and richer – they're clearly in league with the Fairy Godfather.
But in other, more humble places, the price of a peggy collapses. Children in Hull, for example, wake up to an average of just 5p. You're not going to buy too many Kinder Eggs with THAT.
The survey revealed that 61 per cent of parents said their children had a tooth fairy, and after London, the most generous places were Cambridge, which paid £5, followed by Cardiff, £4.75, Liverpool, £4.50 and Manchester with £4.35.
After Hull, the tooth fairy was thriftiest in Portsmouth and York, where it gifted just 10p, followed by Nottingham and Glasgow, with, 11p.
"It seems as though even the Tooth Fairy is feeling the pinch when it comes to certain areas," said Mark Pearson, chairman of the discount website.
"It was a surprise to see some children get as much as £5 per tooth – that's quite a good amount if they put the money by for a rainy day."
Indeed, nice work if you can get it. If only there was a Hair Fairy for every strand we men of a certain age lose on our pillows each night! In fact, there should be fairies for all manner of bodily losses we experience as we grow older. An Eyesight Deterioration Fairy. An I-Used-To-Be-A-Lot-Taller-When-I-Was-Younger Fairy. And surely there has to be room for a Loss of Temper Fairy? This time next year, Rodney, we'd all be millionaires!
So what is the history of the tooth fairy? And why the obsession with teeth?
According to the website ToothFairys: "Many folk cultures marked the loss of a child's baby or milk teeth. Some cultures placed the tooth in a tree or threw it to the sun. Other rituals involved having an adult swallow the tooth or burn it. Even the Vikings had their own ritual called 'tooth fee' whereby a small gift was given to a child when its first tooth appeared.
"The lost tooth is then placed under the child's pillow, in a special Tooth Fairy pillow or container. During the night, the Tooth Fairy visits and makes an exchange - usually monetary - for the tooth."
Another theory goes that ancient Europeans would superstitiously bury their children's fallen milk teeth in the ground around their homes because they believed this was the only way new teeth would grow. But they also believed that if a witch got hold of the tooth, a curse would be placed on the family and so burying it kept the little peg out of the witch's gnarly grasp.
As the Europeans migrated, they brought their rituals with them and at first planted teeth in flowerpots, which eventually led to them being placed under the child's pillow, which parents would replace with a coin. Curious children wanted to know what had happened to their tooth and so the Tooth Fairy was born out of parents' imaginations.
The Tooth Fairy is now as much a part of our culture as Santa Claus and the Easter Bunny. Countless paintings, books and movies have been dedicated to the mythical gift-giver.
A part of our heritage that is now worth its weight in...teeth!