Question

8.) When you look at most people

Answer 1

It appears black because light rays entering the pupil are absorbed by the tissues inside the eye.

When I look at your eye, the light that comes from your pupil is coming into my own eyes along a straight approximately parallel path. From the optics of lenses it is known that light that comes out of a lens in a parallel beam must have originated at the focal point of the lens, that is, in the case when the lens is part of your eye, at the point X in your eye in the diagram below. It is therefore a fact that when you look at someone's pupil, actually you are seeing light that is coming off a point X on that person's retina. But now why is there so little light: in other words, why does the retina look dark, when in fact it is red or even white, in places? The answer is that any light that illuminates point X must have come from somewhere. Apart from some slight scattering of light within your eye, it can only have come into your eye via the pupil. Tracing back the path along which any light that lights up point X must have come from, we see that it must have come exactly along the path that I am looking along: it must have come from the point X' of my  retina!