People observe the clothing and grooming of people in their surroundings, their speech, whether they are perspiring, their skin colour, and skin reactions, as well as their gait and movements. All these observations provide information about sex, race, income, education, social standing, personality, mental state, and health. Many peple also consciously and subconsciously observe the eyes of other people, regarding eyes as windows of the mind. They observe the subtle play of muscle movements around the eyes, the rate at which a person blinks, the level of the eyelids, the volume of tears round the eyelids, the colours of the whites of the eyes, the colours of the iris, and the directions a person is looking. Furthermore, pupil size also influences the reactions of people to each other. For example, a person with narrow pupils is often regarded as hard and unfriendly, while a person with wide pupils is regarded as warm and friendly.

—Dr. G.M. Woerlee, from Mortal Minds: The Biology of Near-Death Experiences, 2003.