The ball was just slightly fuller than the majority. Sneaking ever so slightly from good to full.
There is no doubt that in another over it would have been left alone or defended with confidence and ease.
Joe Root's front foot hesitates for a moment. It's barely visible at full speed, but in our super slow-mo world, you can see it.
Perhaps Root thought the ball from Tim Southee would be shorter. Perhaps the gloom meant he just didn't pick it up quick enough.
By the time Root got his left foot to touch the ground the ball had taken his inside edge.
Once his foot was firmly on the ground, his stumps had been hit.
It was one mistake. One error of judgment. One bit of bad luck.
Had he been later the ball would have gone through to the keeper. Had he got slightly more bat on it the ball would have hit him or gone to square leg. Had he played it like any of the many balls before he would have been fine.
And so, probably, would England.
One good partnership had all but sunk New Zealand. The dour batting of the England first innings had been replaced with a more result-orientated look. They gave New Zealand's bowlers respect, but they forced their way past them. It was a modern performance of grim determination and professionalism that Andy Flower has tattooed on all the England batsmen. It was a partnership built on belief that they were the better side and by sticking around they could outlast and grind out a win.
For three hours they did that. Then Root's foot was slow.
Jonny Bairstow looked jumpy from the start. Where Root and Jonathan Trott had looked like a run-out was their main chance of being separated, Bairstow looked like he could be dismissed in most almost any mode. Yet, his wicket was also unlucky. A ball that would often be called a leg-side half volley won't get him out often. In an empty county ground he would have breezily clipped it off his pads.
Here he missed it, it hit his pads, then rebounded back on to his stumps.
Matt Prior looked lost. An obvious single behind point wasn't just turned down, it was completely ignored. What sort of batsman doesn't take an easy single when they're on a pair? Trott almost ran two runs, and almost ran himself out through the shock of Prior not wanting the run. Prior had his back turned. The next ball Prior played a nothing shot somewhere between attack and anxious that ended in Kane Williamson letting out a squeal.
Next over Prior completed his pair with a limp pull shot.
Trott then had a ball from Williamson that hit a foot mark. That could have happened at any time. Balls from the foot marks had spun a few times during the Test. New Zealand's double left-arm team were also going to make Williamson, and more importantly, Graeme Swann, happy. And with Bruce Martin limping off, Williamson spinning the ball in was always a better chance of getting a wicket from the rough.
Like all offies dream of, the ball spun back through the gate on to the stumps.
The impossible question to answer is if Trott might have covered the spin better had he still been batting with Root. When Root and Trott were there, England looked tranquil, in charge and secure enough to muse about declarations.
With Root out the whole team seemed confused and worried.
Ian Bell's charge down the wicket was bizarre. Steven Finn's single to get off strike was unnecessary. Flower's face was tight.
If the idea of modern sport is to show how confident you are through body language and a serene look of calmness, a photo of Flower's face should be printed out and stuck up in the away team's changing room for Sunday morning. It was the look of a man who may have been thinking of a declaration 40 minutes earlier and was now hoping Finn could help Bell get past a 200 lead.
Flower's face was as telling as the scorecard was: New Zealand were back with a chance to win this Test.
They could thank Root's hesitating foot for opening the door.