One evening I sat down on the green bank opposite this tangle when the low sun behind me shone level into the mass of rock and rough boles and branches, and fixing my eyes on the black centre of the mass I encountered a pair of crimson eyes staring back into mine.

A level ray of light had lit up that spot which I had always seen in deep shadow, revealing its secret.
After gazing steadily for some time I made out a crow's nest in the dwarf pine top and the vague black forms of three young fully fledged crows sitting or standing in it.

The middle bird had the shining crimson eyes; but in a few moments the illusory colour was gone and the eyes were black.
It was certainly an extraordinary thing: the ragged-looking black-plumaged bird on its ragged nest of sticks in the deep shade, with one ray of intense sunlight on its huge nose-like beak and blood-red eyes, a sight to be remembered for a lifetime! It recalled Zurbaran's picture of the "Kneeling Monk," in which the man with everything about him is steeped in the deepest gloom except his nose, on which one ray of strong light has fallen.

The picture of the monk is gloomy and austere in a wonderful degree: the crow in his interior with sunlit big beak and crimson eyes looked nothing less than diabolical.
I paid other visits to the spot at the same hour, and sat long and watched the crows while they watched me, occasionally tossing pebbles on to them to make them shift their positions, but the magical effect was not produced again.
As to the cause of that extraordinary colour in the crow's eyes, one might say that it was merely the reflected red light of the level sun.
We are familiar with the effect when polished and wet surfaces, such as glass, stone, and water, shine crimson in the light of a setting sun; but there is also the fact, which is not well known, that the eye may show its own hidden red--the crimson colour which is at the back of the retina and which is commonly supposed to be seen only with the ophthalmoscope.

Nevertheless I find on inquiry among friends and acquaintances that there are instances of persons in which the iris when directly in front of the observer with the light behind him, always looks crimson, and in several of these cases the persons exhibiting this colour, or danger signal, as it may be called, were subject to brain trouble.