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It's 5:45 in the morning, and in a training field outside Siem Reap, home of Angkor Wat, Cambodia's demining rats are already hard at work. Their noses are close to the wet grass, darting from side to side, as they try to detect explosives buried just beneath the ground.

Each rat is responsible for clearing a 200-square-meter (239-square-yard) patch of land. Their Cambodian supervisor, Hulsok Heng, says they're good at it.

"They are very good," he says. "You see this 200 square meters? They clear in only 30 minutes or 35 minutes. If you compare that to a deminer, maybe two days or three days. The deminer will pick up all the fragmentation, the metal in the ground, but the rat picks up only the smell of TNT. Not fragmentation or metal or a nail or a piece of crap in the ground."

That's right: Someone using a metal-detecting machine will take a lot longer to detect a land mine than a rat using its nose.

There's plenty of work for the rats here in Cambodia. The government estimates there are 4 million to 6 million land mines or other pieces of unexploded ordnance — including bombs, shells and grenades — littering the countryside, remnants of decades of conflict.

Neighboring Vietnam and Laos also have unexploded ordnance left over from the Vietnam War. Dozens of people are killed or maimed in the region every year — and there's a financial toll as well, since the presence of these potentially deadly devices decreases the amount of land available to farmers.

Enter the rats. These are not kitchen rats, but African giant pouched rats, also known as Gambian pouched rats, about 2 feet long from head to tail. Their eyesight is terrible. But their sense of smell is extraordinary. The rats can detect the presence of TNT in amounts starting at 29 grams (about 1 ounce).

A Belgian nonprofit called Apopobegan harnessing the rodents' olfactory prowess 15 years ago. (The group also trains rats to detect tuberculosis). The organization set up a breeding program and training center in Tanzania and began deploying rats to post-conflict countries, first to Mozambique and Angola. Apopo's Cambodia program began in April, in partnership with the Cambodian Mine Action Center.

"The idea was very strange," says operations coordinator Theap Bunthourn. "Cambodian people kill rats, don't like rats. But they're cost-efficient, they're easy to transport, they're easy to train, and they don't set off the mines because they're too light."

That's an advantage over mine-sniffing dogs, also used in Cambodia. And unlike with dogs, says field supervisor Hulsok Heng, bonding is not an issue. "The rat does not belong to anybody, it can work with anyone, not like [a] dog. If [a] handler is sick, [a] dog cannot work with other people. If the dog does not recognize you, it won't work with you. But rat, no problem."

Fifteen rats arrived in Cambodia from Tanzania in late April. Since it's hotter in Cambodia than in Tanzania, Hulsok says, they're put to work before the sun comes up. By midday, it's too hot for them.

One rat, named Victoria, ambles down a 10-yard stretch of grass, tethered to a line held by handlers on either end.

"She's very good today, very fresh after the rain last night," Hulsok says before showing me the mine planted about 7 yards away. As Victoria gets close, maybe a foot-and-a-half away, she stops, sticks her nose up high in the air and seems to lock on to something. She takes another half-step, then scratches the ground. It's the signal that she's found the mine.

"After the rat pick[s] up the scent and scratches," Hulsok says, "we give her a food reward, like a banana."

No TNT, no banana. The rats learn this through repetition. They also learn not to fall for the tricks the handlers use to try to fool them. These can include "the smell from a battery, oil filter, car filter, tuna fish can that we use to confuse the rat," Hulsok says. "Because if they scratch on another smell, we give no food, no reward. Only reward TNT smell."

Another rat, the rock star of the group, named Pit, has already identified two mines this morning. She is just about to reach the spot where they've planted a decoy, known as a "dummy." Pit isn't fooled by the dummy — not even for an instant. She "smells only TNT," says Hulsok.

What about the other rats? "Sometimes they scratch for the dummy. But we don't give them food," he says. "Then the rats will learn. But some rats are more clever than others. Just like people."

Apopo's James Pursey says it costs about 6,000 euros, or $6,500, to train each rat. They can live from 6 to 8 years in captivity. At the Cambodian Mine Action Center training camp outside Siem Reap, it's a pretty good life. The rats are kept in individual cages in an air-conditioned room "because we want to protect our investment, take care of them," says Theap, the operations manager. "We want to keep them good and healthy all the time, so they can perform [with] more efficiency."

There are still some skeptics, even in the demining community, who won't trust a rat. Hulsok isn't one of them. He's been looking for and clearing mines and other unexploded ordnance for more than 20 years. In the case of certain mines, he says, he'd trust a rat over a metal detector any day.

"One type of mine from Chinese, we call 72 Alpha, the metal is very, very small, very, very small detonator and pin," he says. "But a rat can smell TNT very good, so [it] can pick up that mine. But it's good if we have both. Without [a] mine detector, it's not easy to work."

In other words, the giant African rats are just one tool in the demining kit — not meant to replace dogs and machines, but to augment them, helping make it quicker and easier to deal with the legacy of the country's brutal past.

And what happens to the rats when they've reached the end of their working lives?

"Basically, when nearing the end, we notice that they slow down, and we start keeping a close eye on their accuracy via increased field testing," Pursey says. "Eventually, they decide not to come out of their cages and we leave them there for a while until they pass away or they are in obvious distress — in which case, we humanely euthanize them. In those final weeks, they hang out with their mates in playtime and training if they want to, but they don't go out to the field. Normally, they pass away quite quickly once the process has started."

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