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The process takes advantage of the pouched rat’s powerful nose. In the wild, the nocturnal rats use their sense of smell to hunt for nuts, fruits and vegetables in the dark, said Ron Verhagen, a biologist who has studied rodents for 30 years and helped Mr. Weetjens start Apopo.

The bomb-sniffers reproduce rapidly, generating a steady stream of new candidates for the program. But because they are nocturnal, the rats can work for only a few hours in the morning, before the heat becomes too intense.

Mixed reviews

The de-mining community has given the program mixed reviews, questioning whether animals work as reliably and consistently as man-made devices.

“Everybody is trying to look for a magic bullet,” said Andrew Lyons, vice president of the Halo Trust USA, part of an international organization that removes war debris. “Dogs and rats might be cheaper on a square-meter basis, but the constraint is they actually have to work. And in a humanitarian context, they have to work 100 percent” of the time.

The main advantage of using animals is that they focus on the scent generated by a buried explosive, said Perry Baltimore, director of the Marshall Legacy Institute, which specializes in detection dogs. They are not distracted by the countless pieces of metal that usually litter old battlefields, a problem for mechanical metal detectors.

Apopo handlers run many rats over each row in the minefield, in case the first one misses a mine. Although they are not perfect, Mr. Weetjens said, every rat working in the field must first pass a test requiring it to find every mine in a designated area without a single mistake.

At least one organization, Handicap International, is “watching [the rats] with considerable interest,” said Wendy Batson, the organization’s U.S. director.

During a recent trip to a Handicap International program in Mozambique, Ms. Batson made a short side trip to see the rats in action.

“I thought it was really intriguing,” she said. “There’s no question Apopo makes a good case for rats.”

Handicap International uses dog teams in a limited capacity, such as in Kosovo where they will check an area after people have cleared it with metal detectors. Ms. Batson said she thinks rats could play a similar role but only after Apopo produces enough “rigorous test data.”

Rats have several advantages over dogs in Africa, Mr. Weetjens said. Because they are indigenous, rats are much less susceptible to the tropical diseases that can kill foreign-born dogs. While the weight of a dog has on rare occasions detonated a mine, it is virtually impossible for a 5-pound rat to do so.

Mr. Weetjens estimates that the training and deployment of each rat costs $2,000 to $3,000, which includes the handler’s pay. The cost of acquiring, training and delivering a certified detection dog to a site costs about $20,000, Mr. Baltimore said.

“There’s no easy, quick fix to any of this,” Ms. Batson said. “You’re always looking for a balance between safety, speed and cost efficiency. That’s why, of course, there’s always a lot of interest in new techniques that might make it easier and safer.”