The magicicada septendecim is born underground and lives there as a grub sucking juice from the roots of trees. But then, in the spring of its 17th year, it decides it's had enough of darkness, undergoes a metamorphosis and emerges from the soil as a winged cicada.
"Woo hoo," it exclaims to an astonished world, "you forgot about me, didn't you?" It then spends a few brief weeks in the upper world where its mission is to sing, to mate, lay eggs and die, whereupon the world forgets about it again for another 17 years.
In other words the cicada's life cycle is a bit like the Olympics. The Olympic interval is only four years - and most recently five - but that's time enough for us to forget how extraordinary the event is.
According to Sir Arthur Quiller-Couch what distinguishes human beings from the rest of brute creation is that we wear clothes, cook food and speak languages. He might have added that we are unique in enjoying watching fellow members of our species play games. And what games!
Every time the Olympics emerges from its sleep it has grown more wings. This time it's added skateboarding. To lure the boarders the Japanese built them the sort of park that councils normally ban them from, full of steps and railings and low-walled flower displays to slide along the side of.
Normally when adults intrude on teenage games the teenagers flee, and you'd have thought this might be true of skateboarding, which is more an assertion of independence than a sport. The low-slung jeans and the backward cap bespeak a form of resistant grunge.
But the teenagers flocked to Japan. I suppose there's money in it now. As an old person I duly cheered whenever they crashed but they never seemed to hurt themselves. The course needed more concrete.
The first ever gold medal in the women's event went to a Japanese 13-year-old. The silver went to a Brazilian 13-year-old. Peaking that early in life isn't always a good omen.
Fencing's been an Olympic sport for as long as there have been Olympics but that still doesn't make it good to watch. The fencers go on tiptoe like flamboyant musketeers and they dress like electrified beekeepers, wearing a full-facial visor like a fly's eye.
When they manage to stab each other their heads light up, but it all happens far too fast for the eye to see. When they show it in slow motion it still does.
Perhaps the oddest sport is taekwondo. The combatants, wearing plastic helmets and cummerbunds, approach each other sideways, waving before them a raised leg like a prawn's feeler. The idea is to kick or punch the opponent's plastic parts, but to the uninitiated it all seems random.
According to the internet the five tenets of taekwondo are courtesy, integrity, perseverance, self-control and indomitable spirit. From watching the Olympics you wouldn't have guessed.
I watched a lanky American 18-year-old win her gold medal bout and immediately run screaming from the ring to hug her coach, weep hysterically and exclaim "Oh my god" a dozen times, all the while ignoring her disconsolate opponent.
Judokas show how it should be done. Win or lose they keep control of their feelings, peel themselves off the floor and stand to face each other. The referee points in silence to the winner and everyone bows. They then walk to the edge of the floor and bow again. Only when they've left the raised stage do some of them burst into tears. Restraint beats indulgence every time.
For in sport as in art the imposition of limits makes things better. Tighten the form and you heighten the pitch. Loosen the rules and you lose the shape. You can't play tennis with the net down.
Quite how all the different forms of shooting evolved I can't tell you but I can tell you that I spent an hour of my life that I won't get back transfixed by the women's 10-metre standing air pistol. The one skill required for this sport is keeping very still.
I wanted the nice Bulgarian to win but she faltered and the Russian came through and I felt the stab of defeat. But I was only a click of the remote away from becoming engrossed in some other strange activity to which the competitors have dedicated the last however many unseen years before erupting into view at the Olympics for a few brief weeks, to sing, perchance to mate, lay eggs and die.