"It was just wrong place, wrong moment. Just clashed heads with (Wycliff) Palu - he's got a reasonably hard head."
The result: the bizarre sight of a 115kg, 1.93m figure lurching to the ground, trying to get up again, repeating the routine then staggering off in a brave yet futile pursuit of runaway Wallabies wing Lote Tuqiri at Auckland's Eden Park two weeks ago.
"I've seen it on the video a few times. I remember just trying to go and I wasn't going too far," said Hayman, with about as much of a grin as he'll offer in public view.
"That's what you do I suppose, try to catch him. Things weren't working like they should be, so it made it a bit hard."
He said there's been a few jibes from his teammates, from a safe distance of course, that he looked like he was imitating the All Blacks' `down and ups' warmup routine.
Indeed, the concussion which knocked him out during the Philips Tri Nations Test was serious enough to sideline Hayman from last weekend's 45-26 win over the Springboks in Pretoria.
But safely through all the psychometric tests earlier this week, the world's most feared tighthead prop is back to try and cause the Springboks scrum some headaches in Rustenberg on Sunday (NZT).
"I did bugger-all last week then had a run around with the reserves after the game at Loftus. It wasn't until that Saturday I started feeling good and was able to exercise."
Hayman's intent on maintaining the All Blacks' high scrummaging standards as he and loosehead Tony Woodcock are reunited, either side of Taranaki hooker Andrew Hore, who has earned a rare start.
And while the fine and warm conditions and hard ground appear as far removed as you'd get from the ideal prop's scenario, he's got no complaints about the high veldt.
"It's good fun. The games are a lot more open, everyone's a lot more knackered. They're usually high scoring games, there's plenty of tries and plenty of action. Everyone enjoys that."