Emotion is the great disturber of all intellectual operations.

It effects marvellous things, as we shall presently see, in the region of illusory belief, and its influence is very marked in the seemingly cooler region of external perception.

The effect of any emotional excitement appears to be to give a preternatural vividness and persistence to the ideas answering to it, that is to say, the ideas which are its excitants, or which are otherwise associated with it.

Owing to this circumstance, when the mind is under the temporary sway of any feeling, as, for example, fear, there will be a special readiness to interpret objects by help of images congruent with the emotion.

Thus, a man under the control of fear will be ready to see any kind of fear-inspiring object whenever there is any resemblance to such in the things actually present to his vision.