The surprising thing discovered from this study, Masters says, is how often the corpses are not fresh but rather are dug up from the grave in a putrefied or mummified condition. Some even like only the bones. Those who actually feed on decaying dead bodies are known as necrophagists, as opposed to cannibals, who prefer fresh meat or who consume dead loved ones for spiritual purposes. One man merely wanted to eat the nail trimmings from a corpse, another merely to lick the sexual parts—and was still doing so with his exhumed inamorata even as the corpse was falling apart. One woman whose family had mostly died would go into the family crypt to devour the genitals of her male relatives.

"Within the obvious limitations," says Masters, "every sexual act that might be performed with living bodies has been performed also with cadavers."  He claims that women would not derive as much satisfaction as men, since the sexual act is more difficult with a dead male, but he probably had not heard about the pumps that some female morgue workers have devised in recent years to correct this "problem."

Often with such people, their concept of sexuality is somewhat infantile, at least within Masters' theoretical approach. Psychologically healthy people participate in human relationships, he points out, by receiving and giving pleasure. With a corpse, only one gets pleasure, indicating an immature and narcissistic ego.

He notes that other theorists associate this condition with sadism, especially since so many necrophiles seek to mutilate or abuse the defenseless corpse (sometimes only deriving satisfaction from the mutilation). Historical accounts of battles have soldiers with no history of homosexual leanings nevertheless sodomizing the wounded or dead on battlefields. The Marquis de Sade himself wrote frequently about the climax of the sexual act as the death of the partner, and he includes images like orgies atop a pile of rotting corpses, or the use of still-beating hearts or defleshed bones as sex toys.

While Master's and Lea's book focuses on documenting historical cases, psychoanalyst and social philosopher Erich Fromm explains "necrophilism" as a result of social evolution, with the increase in cases occurring as societies evolve toward mechanization and destruction. He writes about what he calls the development of "malignant aggression" in The Anatomy of Human Destructiveness, and his ideas clarify how some people develop a "necrophilous character."  They're guided by a set of values, which are heavily influenced by social circumstances that move them either toward loving life (biophilous) or loving death and demolition. Certain people appear to crave absolute control, for example, developed from a chaotic childhood. The more one wants control, the less one appreciates the evolving and unpredictable nature of life.