In the Winter Olympics, where races can be won or lost by thousandths of a second, tiny imperfections can make all the difference.
Nowhere is this more true than in the ice venues, where skilled technicians called "ice meisters" have honed their expertise over years of crafting the perfect surface.
Make that surfaces: It turns out that all ice is not created equal.
Depending on the sport, the ice might need to be softer or harder, colder or warmer, textured or smooth.
Take long track speedskating, raced on the 400-meter rink at the Gangneung Oval, where ice meister Mark Messer is in charge.
Messer, from Calgary, Alberta, explains that long track speedskating requires the coldest ice of any Olympic sport: between 14 and 21 degrees Fahrenheit.
It's also the hardest ice.
"We're trying to get as little friction as possible," he explains, "so we have to make a balance between grip and glide. We need to have enough grip so that the skate can get a good push off it. But then we want them to glide as far as possible, so that there's less effort expended for the long distance."
Long track ice is built to be about 1 inch thick, and, Messer says, it needs to be as dense as possible to make it stronger. To accomplish that, the ice team filters the water to take almost all the minerals out.
"We leave a little bit in there to kind of hold everything together," he says, "and the other thing that we have to get out is air."
Standing rinkside as skaters take practice runs around the pristine, gleaming Oval, Messer has the look of a satisfied craftsman.
"Yeah, it looks good," he says, noticing a dusting of what looks like light snow kicked up in the corners. "When they're skating and the ice is hard, you get a little puff of snow, and if they're goin' in there and there are chunks comin' out, then we know we've gone a little bit too hard."
Good ice, he says, has a certain sound, too: "Very nice and quiet. If it's not good ice, the blades will kinda grind in the ice. And it's a nice and clean sound here."
Messer, who has made ice in five Olympics, strives for perfection.
"Our mantra is that we don't say, 'That's good enough.' It's always, 'Is that as good as it can be?' And that's what we try to do here."
So far in the Pyeongchang Olympics, long track speedskaters have set six Olympic records on the Oval. Nothing makes Messer happier.
"I still get a thrill when I see people crossing the finish line with a good time," he says. "That's incredible. We take a huge pride in that."
Skaters will tell you they know instantly if the ice is great or not.
"One of the first things we do when we step on the ice is, like, 'How's this ice?' " says Lana Gehring, who's on the U.S. short track speedskating team.
Speedskaters get a lot of information transmitted through a blade that's just a millimeter thick.
"All that input is coming directly up to our body," she says, "so we're able to tell right away if it's dense, if it's grippy, if it's breaky, if it's too rough."
The ice for short track speedskating is thicker and warmer than long track ice. Hockey ice: a bit warmer still.
But in these games, short track speedskating shares a rink with figure skating. Two totally different sports with different ice needs are holding competitions in the same ice arena.
The arena's ice meister, Remy Boehler of France, explains that figure skaters need warmer, thicker, more supple ice so they can dig in for jumps. If the ice is too hard and cold, it will "explode" when they land, he warns. But short track speedskaters need colder, faster ice in that same venue.
It takes about three hours to adjust the temperature from one sport to the other.
The best way for Boehler to tell if he's got it right? "What I use most are my ears," he says. "I use them all the time. When I arrive, I take off my cap so I can really listen to the sound of the blades, if they're gliding or cracking."
And when the ice is great, he can tell by the skaters' faces. They'll take to the ice — and smile.
"That's the best feeling of all," he says.
And then there's ice for curling — a totally different animal.
Look closely at the ice sheets, and you'll see they're not smooth. They're textured with tiny dots called pebbles.
The ice meister of the Winter Olympics curling venue, Hans Wuthrich of Gimli, Manitoba, says his team uses pebbling cans with 25 different pebble heads to sprinkle the ice with droplets. The idea is to reduce friction.
"Those wee little water droplets," he says, "they're the thing that touches the bottom of the curling stone. That's what the rock actually rides on and makes it go easy. And that's also what makes it curl."
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