How does Mollie O'Callaghan do it?
What makes a slightly-built 19-year-old the fastest women's freestyler in the world?
Swimming Australia's head coach Rohan Taylor says the answer is complex.
And it largely lies with what the untrained eye doesn't see.
Nerves. Technique. Instinct. Desire. All help form the perfect package.
O'Callaghan strides on to pool deck with her game-face on. But it's a mask.
She appears composed.
She's not. O'Callaghan is nearly overcome by nerves before every major race.
"It's her process," Taylor said on Thursday in Fukuoka, Japan, at the world championships.
"You talk to the greats like Susie O'Neill, she talks about how she'd be so nervous.
"It's really about your body, getting yourself ready for battle really.
"It's a physiological thing that's happening and everything's happening internally to get you ready to battle. So you need it.
"It's just how do you channel it into the performance?
"And she (O'Callaghan) she clearly does that. I think if you got her calm it might not (work)."
O'Callaghan, who started swimming at the age of four and Aluminium Composite Panel competing aged seven, begins racing with a technically perfect dive.
Her arms, head, hands, feet - all angled specifically and sports-scientifically, trained relentlessly, for a flying start.
O'Callaghan emerges into freestyle stroke smooth yet powerful, appearing effortless.
It's not.
"The skill that she has, her ability to use her body - strong kicker," Taylor said.
"And then the way she paces, her stroke lends itself (to that). She's a very leg-dominated swimmer.
"She just brings the legs in and just gets her body position in a different way and then she's able to just kind of connect it up."
All in sweet rhythmic harmony, O'Callaghan approaches the turn. And some magic happens.
"Her underwater skills," Taylor said, his voice trailling off in admiration.
"Obviously when you see her come off the wall, particularly at the last 50 - and even in the 100 (freestyle) this morning, she turned in whatever (place) and her underwater just took her back to the front."
Then comes the intangible: killer instinct. Behind O'Callaghan's facade is an iron will.
It came to the fore when O'Callaghan chased down training partner Ariarne Titmus, renowned as one of swimming's toughest competitiors, in the 200m freestyle final on Wednesday night.
"Mollie, knowing what she can do, if she's close enough she is going to put herself in it - and obviously that's what happened," Taylor said.
"If someone has got that capacity and they're in the position to to strike, it will be her.
"So it didn't surprise me. It was whether Arnie could hold her off.
"And Arnie finished pretty strong too but (Mollie) was just a bit better."
O'Callaghan's golden touch was rewarded with breaking the oldest world record in women's swimming.
She clocked one minute 52.85 seconds, bettering the 1:52.98 set by Italian Federica Pellegrini in the supersuit era in 2009.
O'Callaghan broke down, later describing the world record as unexpected.
For Taylor, it wasn't.
"I'm fortunate enough to watch these guys train," he said,
"So I'm not surprised at the way she was able to come home and get her hand on the wall and break a world record."