Looking for a way to harness the energy of an unruly German shepherd puppy named Solo, English professor Cat Warren started training him as a cadaver dog. The two have spent the past seven years as volunteers searching for the dead.

In her book, What the Dog Knows: The Science and Wonder of Working Dogs, published this month, Warren tells of her journey into the field of "on the job" dogs and reveals how science is unraveling the secrets of the canine nose.

Not everyone who has a high-energy dog like Solo decides to train him to become a volunteer cadaver dog. What made you decide to teach Solo to look for the dead?

I took Solo to a trainer when he was four months old and asked her what I could possibly do with this dog. She suggested that I could consider training him as a cadaver dog. I didn't even know what that meant. She explained that a cadaver dog goes out to search for the missing and presumed dead.

What makes a good cadaver dog?

Drive, a good nose, and an ability to focus. A good cadaver dog needs to be deeply bonded to his handler and simultaneously be independent and to make decisions on his own. The dog needs to work as part of an inseparable unit with the handler, but also be independent enough that he's not constantly looking back for signals on what to do next. When Solo is working scent, he won't look back at me for minutes at a time. He will be out there, and I will be trying to stay out of his way so he can do his best work.

Do most searches end with finding a body?

Nine out of ten times you search, and you don't find someone. It can be very hard to find the missing. People think that it's easy once you have one or two things in place, but bodies can disappear forever. We're so used to having everything wrapped up in a 50-minute television show that we don't realize how many years investigators can work on cases and how many of them remain unresolved.

Why does law enforcement rely on volunteer cadaver dogs?

It's mostly about budgets. The fact is, cadaver dogs aren't needed every day in the same way a patrol dog is needed every day. There are larger departments that still have cadaver dogs, but more and more law enforcement depends on volunteers. A good dog and handler team can help produce some excellent results.

How does training a cadaver dog differ from training other types of sniffer dogs, like drug- and bomb-detecting canines?

Scent is scent, so the training itself is not greatly different. You introduce the dog to the scent, and you reward him for finding it. You're training a dog to get as close as it can to a particular scent, indicate it's there, and get his reward while making sure that the dog doesn't harm a scene or get harmed. One of the fascinating things about training human-remains detection is that it's a very complex scent. You're dealing with a range of scent, from dry bone to very fresh material. Understanding that and getting the dog to recognize that means going through a pretty long series of steps until you think that you and the dog are dependable. For Solo and me, I didn't rush it. I was inexperienced. We finally were ready when he was about two years old.

How much does science understand about how detector dogs do their work?

What's fascinating about this field is how much we don't know about how dogs detect scent. Chemists are starting to realize what the compounds are in certain drugs that dogs are interested in, but we're still a ways away from knowing exactly what the dogs are alerting on in cadaver scent. Forensic anthropologist Arpad Vass and fellow researchers at the University of Tennessee's anthropological research facility have identified nearly 480 different volatile compounds coming off decomposing bodies. We don't yet fully know which of those compounds are significant to the dog.

Are German shepherds, like Solo, better at detecting certain smells than other breeds?

Despite all the myths about the bloodhound having the best nose versus the German shepherd, we have no really good scientific studies about which breed's nose is the best. There are sometimes more variations between one Labrador and another than between two breeds. Many breeds have fine noses. It also has to do with how much the dog wants to work. You could have a Labrador with a great nose that is indifferent to doing the work, and you would simply never know it had a great nose.

Were you surprised at the innovative ways dogs are being used today?

I was surprised. The tasks that we're thinking up for dogs are multiplying by the day. It's not just bombs, drugs, and humans we're asking dogs to find. They are being trained to detect everything from invasive species to endangered species, from mildew to cows in heat to gas leaks. That's not to say that they're always successful, and we still have a lot to learn about, for instance, how good dogs are at detecting cancer and whether there's ultimately a practical application for that skill. Finally, I think it's important for people to realize that while dogs and their noses are amazing, they are not magical, and it's not easy work. It takes rigorous training, handling, and a fine dog to produce good results.

What's in it for the dogs?

It depends on the dog, but it has to be fun. I think that Solo works partly for the joy of the hunt and partly because he is bonded with me. But I know he loves getting a game of tug most of all.