In this latter instance it must appear very improbable that we are dealing with an instinct that has been built up by slow degrees on account of the benefit accruing at each stage to the individual. In fact, it appears that the instinct is in this case of really no use at all to the animal, for there can scarcely be any question of an escape by this action. Yet so far as we can judge it is the same instinct shown by other animals, and it is not logical to account for its origin in one case on the grounds of its usefulness, when we cannot apply the explanation in the other cases. If this be admitted, we have another illustration of the importance of keeping apart the origin of an instinct or of a structure and the fact of its usefulness or non-usefulness to the organism. Thus under certain conditions this death-feigning instinct might really be of use to the animal, while under other conditions and in other animals it may be of no advantage at all, and in still other conditions it may be a positive injury to its possessor. Perhaps we need not go outside of our own experience to find a parallel case, for the state of fright into which imminent danger may throw an individual may deprive him for the moment of the proper use of those very mental qualities of which he stands in this crisis in greatest need. The peculiar behavior of cattle caused by the smell of blood is another case of an instinct whose usefulness to its possessors is far from apparent. It is known that cattle and horses and several wild animals become violently excited by the smell of blood. Hudson gives a vivid account of a scene witnessed by himself, the animals congregating, “and moving around in a dense mass, bellowing continually.” Those animals that forced their way into the centre of the mass where the blood was “pawed the earth and dug it up with their horns, and trampled each other down in their frantic excitement.”