What the Dog Knows (13 page)

After that, some things go fast and others slowly. Even organs die and decompose at different rates. Hair is one of the last things to go, bones after that, and teeth, which seem so vulnerable while we're alive, hang on forever. This is called the taphonomic process. Bodies become, in the nicest possible terminology, “less organized and more susceptible to outside influences.”

All of it is a complex kind of self-digestion, cellular walls rupturing, everything rich with now-unchecked enzymes. Flies know it. They can locate a body minutes after death. Well-trained cadaver dogs know it's the sweet spot.

A decomposing body, especially outdoors, doesn't automatically smell awful. It depends on the days and months the person has been there; what the temperatures, prevailing winds, and humidity have been doing; and what role insects and animals may have played in that body's progression toward dust. I have stood a few feet from a two-month-old body at a human decomposition research facility and gotten a milky, gassy sweetness up my nose, along with hints of leather and bacon. Someone with a touch of synesthesia appropriately called such a scent “yellowish-orange.” The next instant, the air vortices shifted slightly, and I smelled nothing at all.

Human decay is more marvelously complex and varied than people claim. It's not a scent version of what Supreme Court Justice Potter Stewart said about pornography: “I know it when I see it.”

Except for food, wine, and flora, I don't dwell too much on what I smell. This is not affecting machismo, but something closer to its unbidden opposite: Our brain is hardwired to avoid decay, even Korean kimchi or other fermented delicacies. So while I need to work with training samples without shuddering, I don't spend time wafting them underneath my nose and figuring out their specific bouquets. Inevitably, though, the scent finds its way up my nose. I've smelled enough variants of human decay, or nothing at all, that I would be hard-pressed to narrow the scent down: It's not “unmistakable” and “unforgettable.” Those are emotionally comforting adjectives; we want
human decay to be unique and special. We want to be something more than another rotting organism when we die.

But there are all sorts of human decomposition pretenders out there, not just in the animal kingdom. In the forests of Sumatra, and now in specialty botanical gardens worldwide, there's a decomposition cross-dresser called the corpse flower. It's one of the largest, ugliest, and smelliest flowers in the world. It blooms once every six years. Its scientific name,
Amorphophallus titanum
, means “huge deformed penis.” I'd like to see one, though not smell it. The corpse flower attracts insects, blowflies, flesh flies, and carrion beetles by releasing putrescine and cadaverine. Those chemicals of decomposition are still used for training cadaver dogs, although a number of researchers have established that the chemicals aren't volatile in burials. And they are common. Once you start sniffing, those scents appear everywhere. Some minerals in the red clay of North Carolina vent what smells like death. I've been on more than one futile dig where the crime scene investigators say they clearly smell human decomposition and find nothing.

Although it has been around as long as we have, few researchers know much about the scent of human death. For all the attention that a forensics show like
Bones
receives, and as much as forensic scientists know about maggots, skin slippage, and the thermodynamics of putrefaction, the work on the volatile compounds that vent off human decomposition is just starting. Despite some early medical fascination and training with the smell of death, for most modern scientists and chemists, “odor mortis” is a new frontier. Forensic anthropologist and research scientist Arpad Vass and his colleagues have identified nearly 480 different volatile compounds coming off decomposing bodies. Arpad thinks it will be closer to 1,000 organic compounds (though not all of them volatiles) by the time they are finished creating a DOA database—which in this case stands for “decomposition odor analysis,” not “dead on arrival.” As Arpad noted with his slightly inflected German accent, the decomposing human is “a pile of pollution.”

Why bother sorting out the chemicals from that messy pile? Because
ultimately, the knowledge may help create a machine that can help detect the smell of death. It may help scientists develop more effective pseudoscents for dogs to train on.

If it's a new frontier to figure out what compounds are in the air column from human decomposition, it's another stratospheric leap to understand what the dog's nose is picking up from that air column and translating as human remains. No one knows exactly what the dogs are smelling. We can't ask them. Most likely, they are smelling a lot of things mixed together.

“It's a much more complex chemical composition than any other forensic sample, with the possible exception of human scent,” said Florida International University analytical chemist Kenneth Furton. He and a group of scientists, trainers, and law enforcement representatives are trying to develop a national set of best practices for detection dogs. Creating a set of best practices is a challenge, and understanding how best to train dogs to detect human decomposition is one of the group's biggest challenges. “There are more knowledge gaps in human-remains detection than anywhere,” Furton said.

The things that we humans invented—bombs, manufactured drugs, and land mines—are chemically simple in comparison to our remains. Decomposing humans are not entirely a black hole, though. While no one has yet nailed the perfect formula for what it is that good cadaver dogs think is unique or interesting about dead people—as compared with, for instance, garbage from a suburban household—we do know that solidly trained dogs can tell the difference between dead human, dead deer, and aged goat cheese, or something equally putrefied and odiferous. Arpad noted that cadaver dogs tend to alert on dead sheep more than on other species; he thinks some dogs get confused by the generous dose of sulfur that sheep emit after they die. We emit it, too.

Although sheep may be chemically close to humans, there are, he notes, several significant chemical differences between us. Chemicals we ingest may play a role. Arpad's research laboratory, along with one
or two others, found tantalizing evidence that compounds we swallow or inhale—from fluorinated water to asthma inhalants—may play a role in our unique smell after death. It's not much of a stretch to think that our decaying bodies might whisper more than a hint of je ne sais quoi of chemical compounds we've steeped our bodies in during our lifetimes.

“We take in a lot more chemicals than we should,” Arpad said. The unanswered question is whether those translate to volatile compounds significant to the dog, even though the carcinogenic compound carbon tetrachloride seems to jump out when Arpad takes air measurements of human decomposition.

We have a fair amount of evidence that dogs do fine at detecting remains that are hundreds of years old—long before fluorocarbons and freons and fluorinated compounds and solvents and poisonous cleaners and antibiotics came on the scene. In rural areas where water isn't fluorinated, dogs can find people who have mostly drunk well water all their lives. Domesticated pets ingest plenty of fluorinated city water and chemicals, and well-trained dogs don't alert on their remains.

Arpad believes they are getting close to knowing what dogs find important and unique about human remains. The chemical portrait gets blurrier with buried bodies, which may be emitting different volatiles than surface ones. He thinks he knows what volatiles dogs are alerting on in burials—perhaps as few as thirty compounds—but he's not yet tested the theory. Those volatile gases have to be available at the soil surface for the dog's nose to collect. Even bone has twelve detectable volatile compounds.

It is possible that a unique volatile compound—something that barely registers on the gas chromatographs positioned around bodies in Arpad and his colleagues' experimental research plots—hits the dog's nose and lights up her brain like a pinball machine. Or it could be a few compounds, or a bunch of them in various delightful combinations. When you combine the variety of conditions under which dogs find human remains, from freshly deceased to hundreds of years
old, the options become dizzying. For instance, Arpad notes, the odor profile for a body that has all the busy microbes associated with the digestive system working overtime is very different from the profile for scattered limbs.

While we don't know the exact compounds they are smelling, dogs find human remains. That should count for something. Just because dogs find the dead without an utterly coherent scientific theory as to why, and without an easy way to test it under controls, doesn't mean it's not happening.

Cadaver dogs' ability to find human remains may be analogous to humans' ability to recognize faces. Researchers don't have a clear understanding of how facial recognition works, but people do it effortlessly, at all angles, even in bad light. Trying to break that recognition down into parts (it's those great cheekbones!) doesn't work. It's the whole face. Machines still aren't nearly as adept at facial recognition.

So the two scientific arenas—what volatiles in what percentages are involved in human decomposition itself, versus what volatiles dogs react to as cadaver scent—may overlap a great deal. Or not. Who cares? Well, we like to know things. It might help us figure out why some dogs are drawn to rotting trees like sycamores or to the vegetative decomposition in swamps. Isolating what the dogs find significant in decomposing humans might help handlers and trainers identify which training aids are best and the ideal way to store them. Ultimately, that knowledge might lead to finding substitute training aids that are legal, safe, and much closer to the real thing than the pseudoscents or other chemicals in current use.

This new research arena has started to upset old beliefs. Some trainers and handlers—more in the past but a few in the present—have claimed that pig samples are the next best thing to human samples for cadaver-dog training. The temptation is great. Pigs are plentiful and a forensic fallback, a model for studying human disease and decay. No ethical fuss or muss about using them as training aids: Just pick
up some pork spareribs from the grocery meat counter. Yet, as Arpad Vass noted, there's a vast difference between the chemical profiles of deceased humans and swine. “Pigs smell quite different from humans. We have this well documented.”

Nancy Hook scoffed from the beginning of training about handlers using pig tissue as training samples. It was pretty simple to her: “Pigs aren't people.”

Mary Cablk, an associate professor at the Desert Research Institute in Nevada who trains cadaver dogs and does research on the reliability of detector dogs, took the pig problem a step further. She and her analytical chemist husband, John Sagebiel at University of Nevada, Reno, compared the volatile organic compounds of chicken, cow, and pig with those from human remains. Their results should be the final nail in the coffin for an entire cadre of trainers and handlers who have said for decades that pig samples are the next best thing to human samples for training. Their research shows that we humans smell much more like chicken than pig when we decompose. If it's any comfort, we smell like organic chicken from Whole Foods.

•  •  •

 . . . and suddenly, coincident with death the beam end dropped with an audible stroke hitting against the lower limiting bar. . . . The loss was ascertained to be three-fourths of an ounce.

—Duncan McDougall, MD, “Hypothesis Concerning Soul Substance,”
Journal of the American Society for Psychical Research
, 1907

Cadaver-dog handlers and trainers have watched dogs find human remains for several decades. No matter. No rigorous scientific studies had shown how well dogs could do it. They just did it: Dogs were indicating that they smelled human decomposition. No one knew exactly what they were alerting on, unless a body, or a part of a body, was there as undeniable proof. What part of the part, though, were they alerting
on? How soon after death could dogs detect something? How long after death did the scent last? And what, for a dog, was that “scent”?

Despite numerous studies of how working dogs reliably detect drugs and bombs, few scientific studies have featured cadaver dogs. It's messy work, and the real-world aspect can irritate scientists in search of conclusive data. It's hard enough figuring out how a narcotics dog can find pure heroin; figuring out how cadaver dogs can find the infinite variables of dead humans seems impossible.

Scientific uncertainty hasn't kept people from using dogs worldwide to help pinpoint the perfume of death, from the faintest emanation off a tooth to the fulsome scent that lofts from an entire body. A few small studies existed here and there, like Debra Komar's 1999 study on cadaver dogs' ability to find scattered human remains in Canada, and another in 2003 on dogs' finding buried remains in the southeastern United States. That 2003 study noted quite accurately that “dog handlers affected the reliability of the cadaver dog results.”

It was far past time, at the beginning of the twenty-first century, for someone to come up with a controlled scientific study on cadaver dogs' capacity to detect the faintest smell of death. That was when an unfortunate series of events—almost always the case when cadaver dogs are involved—created a perfect opportunity for imagining, then realizing, a small, elegant scientific study.

A wife in Hamburg, Germany, disappeared off a yacht in 2005 while sailing, apparently not entirely happily, with her husband. The husband reported her missing. She must have fallen overboard, he said. When the Hamburg state police sent one of their cadaver dogs onto the boat, the Belgian Malinois aggressively communicated to its handler that something bad had happened on the mattress in the yacht's bedroom.

There was no body in the bed. No blood. No tissue. It must have been a soupçon of scent that caught the Malinois's nose. Who knows? Mattresses can be funky places, even on the best yacht. Regardless, without a body, tissue, or blood, there was no case.