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).

After a few hours of training and sniffing for explosives, Leyla the rat follows her handler. The rats socialize for a bit before retiring to their cages for the rest of the evening.

After a few hours of training and sniffing for explosives, Leyla the rat follows her handler. The rats socialize for a bit before retiring to their cages for the rest of the evening.

Michael Sullivan for NPR

A Belgian nonprofit called Apopo began 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."

But that's a long way down the road for Victoria, Pit and the other newly arrived rats. They have a lot of work ahead of them, a lot of lives to help save. Theap hopes they'll be deployed in real minefields by September or October.

Copyright 2015 NPR. To see more, visit http://www.npr.org/.

Transcript

STEVE INSKEEP, HOST:

We have surprising news this morning that rats save lives. They're doing that in Cambodia, where it turns out that rats can help to locate long buried landmines. Now that I know this, I never have to worry about landmines in my neighborhood again. Michael Sullivan reports from Cambodia.

MICHAEL SULLIVAN, BYLINE: Most rats you want to catch, and then - well, never mind. But these rats, these rats you want to let out of the cage. This morning, that's about 5 a.m. And they get to work quickly, their noses close to the wet grass as they search for explosives buried below. The on-site supervisor, Hulsok Heng, charts their progress on a clipboard.

HULSOK HENG: They are very good. You see one - 200 square meter - they clear about only 30 minutes or 35 minutes. If you compare to deminer, maybe two day or three day.

SULLIVAN: That's right. The guy with a metal-detecting machine will take a lot longer. And that's because...

HENG: The deminer, they will pick up all the fragmentation, all metal in the ground. But the rat, they pick up only the smell of TNT. They not pick up the fragmentation or metal or nail or piece of crap in the ground.

SULLIVAN: The rat is not going to be fooled by a battle cap, a nail, none of that.

HENG: Yeah, none of that.

SULLIVAN: Only explosives like TNT. These aren't kitchen rats. They're African pouched rats. And they're monsters, about 2 pounds each and 2 feet long from head to tail. They don't see very well, but their sense of smell is fantastic. And a Belgian NGO, Apopo, has taken that idea and run with it, dispatching rats from its training center in Tanzania to post-conflict countries - first in Africa, Mozambique, Angola and now Cambodia, where decades of conflict ended only recently and left the country littered with unexploded ordinance - according to the government's estimates, millions of mines, bombs or shells.

HENG: (Foreign language spoken).

UNIDENTIFIED MAN #1: (Foreign language spoken).

SULLIVAN: Hulsok Heng says the rats have a leg up on mine-sniffing dogs, too, because dogs bond with humans - rats, not so much.

HENG: If it's a dog, they recognize the handler. If the handler's sick, that dog cannot work with other people. With the rat, anybody can work with - they cannot recognize the handler. So anybody can use the rat.

SULLIVAN: And a rat won't set off a mine if it steps on one accidentally - not heavy enough - a mine-sniffing dog, problem. One of the rat wranglers here, Sean Na, has worked with both and says there's another advantage to rats.

SEAN NA: (Foreign language spoken, laughter).

SULLIVAN: Na says the rats don't bite as hard. I walk with Hulsok Heng to a 200-square meter area roped off with measuring tape to have a look at one of the rats at work.

OK, who do we have here?

UNIDENTIFIED MAN #2: (Foreign language spoken).

HENG: Victoria.

SULLIVAN: So here's the test now - right now - for Victoria. About 1 meter from where we're standing, you have planted a mine. Let's see if she finds it.

HENG: Yes.

SULLIVAN: Victoria ambles down the line she's tethered to, nose to the ground, then stops and pushes her nose high up in the air, sniffing repeatedly until she locks on. Then, she takes one more step and scratches the ground.

(CLICKING)

SULLIVAN: So that click we just heard was the sign for the rat to come and get the banana...

HENG: Yes.

SULLIVAN: Because she scratched the ground when she found...

HENG: Yeah. After the rat pick up and they're scratching, we click. And then we give food reward, like banana.

SULLIVAN: No TNT, no banana. And to make sure the rats get it, the handlers plant dummies. Next to Victoria's patch, there's another rat working named Pit.

HENG: So they finish two mine already. So that the black number seven, this is the dummy. Dummy, that mean the smell from battery, car filter, oil filter, tuna fish can, that we make to confuse the rat.

SULLIVAN: You're trying to trick him.

HENG: Yeah because if they scratch on other smell, we don't give food.

SULLIVAN: Pit walks the line and doesn't go for the fake. A few meters down the line, though, there's another mine. And this one's no dummy. It's packed with explosives. Pit stops, sniffs and quickly scratches the damp earth.

(CLICKING)

SULLIVAN: Hulsok Heng just smiles.

HENG: He never found the dummy. He smell only TNT.

SULLIVAN: He's never fallen for a dummy?

HENG: No, never.

SULLIVAN: And the other rats?

HENG: Sometimes, yeah. Sometimes they scratch for a dummy, but we don't give them food. Then the rat, they learn. But some rats, they are more clever than the other.

SULLIVAN: And what happens to a rat who's not clever and is lazy too? Do you just give them to the cat?

HENG: No (laughter) we keep training and training.

SULLIVAN: That training, according to the Apopo website, costs about $6,500 all in. But the rats have a long lifespan, about 8 years, and low maintenance.

HENG: Because they eat only banana - one banana or two banana a day. That's it. And they never get sick.

SULLIVAN: We go back to the office for a look at the rats' spacious, air-conditioned cages. First impression, these rats live better than a lot of people in Cambodia. The boss here, Theap Bunthourn, doesn't disagree.

THEAP BUNTHOURN: We want to protect our investment. We want to keep them good, healthy all the time so that they can perform in a field more efficiently.

SULLIVAN: There are still some skeptics out there who just won't trust a rat. Apopo field supervisor Hulsok Heng, who's got 20 years' experience looking for and blowing up mines and other ordinance, isn't one of them. In fact, he says, there are some things the rats can do that metal machines can't.

HENG: One type of mine from Chinese, we call 72 Alpha - the metal very, very small. But for the rat, they smell the TNT very good. So they can pick up that mine.

SULLIVAN: So you would actually trust a rat's nose over a metal detector in that instance.

HENG: Yeah, but if you have both, it's very good.

SULLIVAN: In other words, the giant African rats are just another tool in the demining box - not meant to replace dogs or machines but to augment them, to make it quicker and easier to deal with the legacy of the country's brutal past, a legacy that still kills or maims dozens every year. Coordinator Theap Bunthourn says he hopes his rats in training will be deployed for real come September. For NPR News, I'm Michael Sullivan outside Siem Reap, Cambodia. Transcript provided by NPR, Copyright NPR.

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