If the answer to this question was known, the bloodhounds would easily find the bodies of the dead by smell. But so far, scientists do not know the universal set of odors common to every human body after death, and this is a big problem for forensic scientists and rescuers.
The search for a specific "smell of death" is not an impossible one. The main thing is known: the smells that the body emits after death are specific to each type of living creature. It is known, for example, that in the initial stages of decomposition, the human body begins to secrete putrescine and cadaverine, better known as cadaveric poison. However, sensors do not always detect this substance near the body.
Other substances accompany the human corpse in almost all circumstances: toluene and P-xylene. The first gives death a subtle smell of paint thinner. The second one smells sweetish; it is the most recognizable and most often unpleasant for people. Often in the air next to the deceased, molecules of another substance are found - diethyl sulfide, the unpleasant aroma of which resembles the smell of garlic.
The training of bloodhounds is complicated by the fact that scientists do not know what substances the smell of the body is made of.
To teach a dog to search for the dead, you need to give a sample, the smell of which will be guaranteed to be present in the smell of any dead body. However, this is not so simple: the dead smell differently depending on the cause of death, lifetime diet and other factors. Snoop dogs are now allowed to sniff pieces of pork or, if possible, samples of human tissue.
If chemists manage to describe and compose such a universal smell of a dead person, the need for pork and fragments of human bodies will disappear. Moreover, it will be possible to stop endangering the lives of four-legged animals, and instead use drones with sensitive "electronic noses" tuned to search for the "smell of death."