There is one kind of object in the presence of which no man remains indifferent and which evokes in almost all men the same emotion, namely impending danger; hence the sudden appearance of imminent danger may instantaneously convert any concourse of people into a crowd and produce the characteristic and terrible phenomena of a panic. In each man the instinct of fear is intensely excited; he experiences that horrible emotion in full force and is irresistibly impelled to save himself by flight. The terrible driving power of this impulse, excited to its highest pitch under the favouring conditions, suppresses all other impulses and tendencies, all habits of self-restraint, of courtesy and consideration for others; and we see men, whom we might have supposed incapable of cruel or cowardly behaviour, trampling upon women and children, in their wild efforts to escape from the burning theatre, the sinking ship, or other place of danger. The panic is the crudest and simplest example of collective mental life. Groups of gregarious animals are liable to panic; and the panic of a crowd of human beings seems to be generated by the same simple instinctive reactions as the panic of animals. The essence of the panic is the collective intensification of the instinctive excitement, with its emotion of fear and its impulse to night. The principle of primitive sympathy[15] seems to afford a full and adequate explanation of such collective intensification of instinctive excitement. The principle is that, in man and in the gregarious animals generally, each instinct, with its characteristic primary emotion and specific impulse, is capable of being excited in one individual by the expressions of the same emotion in another, in virtue of a special congenital adaptation of the instinct on its Cognitive or perceptual side. In the crowd, then, the expressions of fear of each individual are perceived by his neighbours; and this perception intensifies the fear directly excited in them by the threatening danger. Each man perceives on every hand the symptoms of fear, the blanched distorted faces, the dilated pupils, the high-pitched trembling voices, and the screams of terror of his fellows; and with each such perception his own impulse and his own emotion rise to a higher pitch of intensity, and their expressions become correspondingly accentuated and more difficult to control. So the expressions of each member of the crowd work upon all other members within sight and hearing of him to intensify their excitement; and the accentuated expressions of the emotion, so intensified, react upon him to raise his own excitement to a still higher pitch; until in all individuals the instinct is excited in the highest possible degree.