All these devices for the avoidance of danger and escape from death could have been developed in animals before these had any distinct idea as to what death was. We know that some animals can distinguish between living and dead prey. Some carnivora recognise the smell of dead bodies. Those which are accustomed to feed on living creatures refuse all others, detecting the difference by the absence of movement. As in such cases the idea of death is imperfect, it is easy to deceive the creatures by offering carcases artificially set in motion, or living prey rendered motionless by some means or other. In order to escape from enemies so readily imposed upon, many insects when alarmed become motionless and feign death; and that may be regarded as yet another instance in the category of natural means for the protection of individual life. Moreover, the higher animals, such as mammals, exhibit a profound ignorance of death, many of them remaining completely undisturbed in the presence of dead companions, or even devouring the latter at the risk of contracting a fatal disease. Rats, for instance, eat the bodies of rats which have died of plague, and while appeasing their hunger themselves contract the disease which they transmit to other animals, particularly to human beings. Unlike those animals, however, which are indifferent to the death of their kind, there are others that instinctively shrink at seeing the dead bodies of their own species. Horses on passing a dead horse show signs of discomfort, and attempt to run away. Bullocks when witnessing the slaughter of others also exhibit evidences of distress and fear. In spite of these examples, however, it is quite certain that animals, even those highest in the scale of life, are unconscious of the inevitability of death, and of the ultimate fate of all living things. This knowledge is a human acquisition. In man, the instinct of self-preservation is well developed. Hardly appreciable during infancy, it manifests itself in a marked degree in young children. At the sight of a human corpse, children become panic-stricken, as though confronted by a wild beast or snake.