This principle of direct induction of emotion by way of the primitive sympathetic response enables us to understand the fact that a concourse of people (or animals) may be quickly turned into a panic-stricken crowd by some threatening object which is perceptible by only a few of the individuals present. A few persons near the stage of a theatre see flames dart out among the wings; then, though the flames may be invisible to the rest of the house, the expressions of the startled few induce fear in their neighbours, and the excitement sweeps over the whole concourse like fire blown across the prairie. The same principle enables us to understand how a few fearless individuals may arrest the spread of a panic. If they experience no fear, or can completely arrest its expressions, and can in any way make themselves prominent, can draw and hold the attention of their fellows to themselves, then these others, instead of perceiving on every hand only the expressions of fear, perceive these few calm and resolute individuals; the process of reciprocal intensification of the excitement is checked and, if the danger is not too imminent and obvious, the panic may die away, leaving men ashamed and astonished at the intensity of their emotion and the violent irrational character of their behaviour. Other of the cruder primary emotions may spread through a crowd in very similar fashion, though the process is rarely so rapid and intense as in the case of fear[16]. And in every case the principal cause of the intensification of the emotion is the reciprocal action between the members of the crowd, according to the principle of sympathetic induction of emotion in one individual by its expressions in others.