Because their eyes are made highly sensitive to small quantities of light. It is also believed that there are certain properties of light which affect their eyes, but do not affect ours. In other words, that there are some rays which are luminous to them which are not luminous to us. Hence they find light in what we call darkness.
"He that hath ears to hear, let him hear."—Matthew xi.
982. Why does the pupil of a cat's eye appear nearly closed by day?
Because the cat's eye is so sensitive to light that the iris closes the pupil almost entirely to shut out the too powerful light.
CHAPTER XLIX.
Because the tympanum of the ear receives impressions from sounds, and transmits those impressions to the brain in a similar manner to that in which the retina of the eye transmits the impressions made upon it by light.