Consider, for instance, the behavior of your average ant. If an ant is trapped in sand, its fellow-ants will attempt to save its life, pulling on its limbs and digging away at the sand to try to free it. And if an ant dies inside its colony, other ants, acting like tiny insect undertakers, will swiftly remove the body, often taking it to a designated location outside the nest. At first, those behaviors seem to suggest that ants understand death, since they react appropriately to both its imminence and its actuality. But in reality the ants are only responding to certain chemicals—in the first case, one that serves as a kind of distress call, and, in the second, ones emitted by a carcass. If you take a live ant and dab those carcass chemicals on it, as E. O. Wilson did in the nineteen-fifties, other ants will treat it as dead and promptly carry it out of the colony, even if the alleged corpse is waving its antennae, resisting its would-be pallbearers, and otherwise displaying every possible sign of life.

The ants, in other words, have no concept of death; their reaction to it is governed solely by instinct. We can recognize such reactions, Monsó explains, because they are automatic, provoked by specific stimuli, and entirely predictable: each individual ant will always react the same way when confronted with death, and every ant will exhibit the same behavior as its peers. By contrast, animals with a concept of death will react to it in ways that are learned rather than instinctive, not rigidly responsive to specific stimuli, and highly variable: the same individual will react differently to different deaths, and different individuals will react differently to the same death.