Pencil sharpeners, museum toilet paper, garden gnomes. Chopstick wrappers, old socks, shrunken heads. Across the world, people tend to collect rather strange things. So does Rafael Nadal, but his addiction is slightly healthier - it involves collecting victories in the dirt. What else would you expect from a gladiator?
Tennis' highest winning rate on carpet is .853 by John McEnroe, on hard courts it is .840 by Novak Djokovic, on grass it is .912 by Don Budge but on clay it is .917 by Nadal. To call him the greatest player on clay is insufficient. In fact, he is greater on clay than anyone else has been on anything else in the history of tennis.
Sport generates waves of numbers every day and we surf on them till they don't interest us any more. We might think 200 is cool, which in yards is roughly how far Alan Shepard hit his second golf shot on the moon. We might consider 64 to be freaky, which is the number of degrees a MotoGP motorcycle can lean without falling over. But, as Nadal will testify, there is no number quite as strong and as snazzy as 10 which, as of last Sunday, is how many titles he has in Barcelona.
And, well, Monte Carlo, too. And soon, possibly, the French Open.
Ten has been taken seriously as a number since the plagues visited and commandments arrived. In sport it has historically represented toughness, for it's the number of events in the decathlon and the seconds a downed boxer has to return to his feet. Ten is also an invisible barrier, as every 100m sprinter stuck at 10.01 seconds will tell you.
Ten is exactly how many men Manchester United needed to beat Arsenal in their 1999 FA Cup replay and the number Reggie Miller summoned when he had to emphasise a point. Said the basketballer once on a radio show: "Michael Jordan on his worst day is 10 times better than Kobe Bryant on his best day".
Ten is the holy number on the back of a football shirt, though the first, celebrated wearer of it, that Pele guy, reportedly noted that it was a legend born from luck. "I was just 17 in 1958 and the numbers were drawn. I got No. 10 and that's how it all started."
Ten, of course, is perfection, it is sporting divinity, it is the number we hold up almost in surrender when confronted with flawlessness. In 1982, diver Greg Louganis got an unequalled perfect 10 from all seven judges in the world championships. In 1976, it was the only number that judges could summon up after watching Nadia Comaneci on the uneven bars at the Montreal Olympics.
Comaneci was probably stunned because she told Reuters last year that she felt - and athletes instinctively know how a performance has been - her routine was imperfect. "I thought I did a pretty good routine but I didn't think I did my perfect routine. I know I didn't watch the scoreboard as I was already thinking about the balance beam after I finished."
But now have come two 10s in tennis which are equally mesmerising. If Nadal adds Paris to Monte Carlo and Barcelona it will be a tennis triptych that will hang untouched in history for a while. Yet to have done it once, let alone twice, is extraordinary if you consider he has no real rivals in tennis' record books.
Ten titles in one geographical location is seriously intimidating. It is two more than Milos Raonic has won across the entire globe and it is double anything that John McEnroe ever collected at a single event. Novak Djokovic at least has six, at the Australian Open, Miami and Beijing.
In the old days, at Wimbledon, the champion only played a single match - the final. Still, William Renshaw could only collect seven titles, a feat equalled by Pete Sampras who had to sweat the entire fortnight. Further away in Europe, it was at a very distinguished German address - Roger-Federer-Allee 4 - that a Swiss fellow won eight grasscourt titles in Halle.
But no one is Nadal's equal. He is first because somehow he lasts. His multiple 10s are a blend of excellence and consistency, stubbornness and survival. More than just a player, he seems in some ways to be an explorer, venturing where no athlete has. The Reinhold Messner of the dust.
The first year Nadal won the French Open, 2005, was the first year he won Barcelona and Monte Carlo. He won eight clay events in that year -Federer has 11 in his lifetime - and it was a time so long ago that Asafa Powell was setting the world 100m record and that Lance guy was cheating his way to the Tour de France.
Now Nadal is still running. He's chasing the French and you can see it in the face of this man whose entire career has seemed like an endless resurrection. If you consider the rebellion of his body, it seems preposterous he found time to collect 10 of anything beyond MRIs. Perhaps only the poets know the answer to such men, or as Alfred, Lord Tennyson, taking refuge in numbers, once wrote:
My strength is as the strength of ten/ Because my heart is pure.