When does a golf shot have the effect of the dive of a hawk or the turn of a great thoroughbred's hoof or a punch delivered by someone like Muhammad Ali. If we didn't know before, we knew in a moment that stretched credibility in another high noon of burning heat yesterday. It is when it is made by Tiger Woods.
Woods has long been a contender for the most fabled and improbable of titles, that of the greatest sportsman of all time - a man who, in the impact he has had on his own sport, in his ability to squeeze out the pips of all opposition, has transcended every game we play.
This was a view that was as dramatically reinforced yesterday as any point in Tiger's mastery of modern golf. By the end of the day, he had just the margin of a shot between him and a resurgent Ernie Els, but then you had to consider the shot. It was one of the greatest anyone had ever seen.
Of course there had been so many examples of the sublime talent of the Tiger. His extraordinary chip across the moonscape of the 16th green at Augusta last year seemed to have explored the very limits of golfing possibility. But on that occasion the tough pro Chris DiMarco found the nerve to fight back, at least to the point of a play-off.
In two previous Opens he has pummelled down the opposition in great sweeps of accumulating power and virtuosity. But here yesterday, on the 14th hole, it seemed that he had gone further than that; it was as though he had simply drained away the idea of authentic competition.
Of course there might be eruptions of resistance. Someone might come bobbing, optimistically, out of the pack and show a brave face. But then suddenly it was hard to shake the belief that at the essence of the 135th Open there was really only one man.
Historically, the Tiger's 212-yard, four-iron eagle inevitably placed itself beside the famous Golf Shot Heard Around the World, Gene Sarazen's albatross at the 15th in the infant days of the US Masters. Certainly, you had every reason to order up a brass plaque - as they did a little way up the coast at Royal Birkdale, when Arnold Palmer once drove improbably, volcanically, out of the rough.
Yet this was so much more, you had to believe, than a single statement about the force of random inspiration.
It came from a body of work that has become stunning here... a piece of course management that in competitive terms suddenly began to look like nothing so much as the invasion of the psyche of 155 rivals by a player operating on his own terms and with his own vision of what could be achieved.
When the galleries exploded as Woods sank his shot, and Nick Faldo, a once great champion fighting now for nothing more than a chance to beat the cut, appealed for a little quiet, it was clear the sky-splitting cheers reached beyond one mere moment of sporting excellence.
They were about a sportsman claiming an extraordinary destiny, one announced nine years ago when he won the US Masters - as a 21-year-old - by such a margin that the quest seemed not a maiden major victory but the very re-defining of the game.
Now, here, he has made what many hard judges can only see as the decisive move towards his 11th major - a total which leaves him just seven short of the total of 18 by Jack Nicklaus, a mark that before the arrival of the Tiger had long been been assigned to the realm of the insurmountable.
But whatever the years bring, whatever challenges - and none had risen more strongly than that of the Tiger's compatriot Phil Mickelson - it seems that Woods always has another level of resilience, and resource.
Yesterday in the wake of that shot which gave him a three-shot lead and another surge of belief in a unique destiny, he agreed with some serenity that he had rarely ever enjoyed such a zone of comfortable creativity.
He spoke like a man who had suddenly been presented with a million options, all of them supremely negotiable, He was asked if he had ever used irons with such easy, brilliant authority; if he had ever conjured shots which moved on such a perfect line. "Yes, but maybe only once," he said. "At Pebble Beach in 2000."
That was the occasion of his third major triumph - the US Open. Though the brilliance of a recently faded challenger, Els, re-surfaced in the cool of the evening, it was still difficult to believe that the Tiger had not done the imperious groundwork for the 11th win - and another stride closer to Nicklaus.
Tiger said: "My best ever work with irons? OK, I felt like - to be very honest with you - I really controlled my flight.
"I really felt I was able to shape the ball both ways, and really control my trajectory. Sometimes it was higher than others, sometimes really low. But I was able to hit the golf ball on the flight that I really wanted to.
"When you are doing that you can look at your shots and see that they are mostly pin-high. It's awfully nice to do that on a links course. It's not easy to do on such a course. It's easy when it's plugging up there, but when you have to control the bounce on the greens and the fairways, yeah, I really felt I was in control of my flight today."
The belief that you are in charge of your own world, that you can do more or less anything you want, has maybe been put more lyrically, but the meaning of Woods yesterday went so much more deeply than the rhetoric of mere self- confidence.
It said much for the competitive honesty of Faldo that he was, despite his own disappointment, the first to recognise the extraordinary aura of the man who had treated him so coldly for two days.
"He's the best," Faldo said. "He's mentally the toughest. He's the most trained for what you have to put up with. He plays from the first tee with the 'Tiger Show' for 72 holes. All of a sudden the guys who play with him tomorrow are going to get out there with 60 cameramen and it will be a different world for them, and he is in the same mode all the time. That's what the great champions of any sport have: Bjorn Borg and others have been able to do this. They are in the same mode from the moment they walk out until the moment they finish."
Among the last of the viable challengers last night was the beautiful ball-striker Els, who drew within a shot of Woods at the end of a round which had seen a return to some of his most beautiful touch.
However, even as Els made his move quite majestically, there was still reason to tremble for his fate.
In the past he has admitted that the mere presence of the Tiger is enough to paralyse the greatest talent. Like Woods, Els had shot 65, had announced some of the form of his life. But he knew he had to take another vast step this morning.
The South African had to convince himself that, man to man, hand to hand, he could maybe beat arguably the greatest golfer we will ever see.