Let's learn more about the Human Eyes.
One important part of the eye that we see every day is the Pupil.
The pupil is the big black circle in the middle of the eye.
Even though it looks like it is painted black, the pupil is actually just a hole!
There are parts covering the pupil, and parts of the eye behind it.
This hole in your eyeball gets bigger and smaller to let in more or less light depending on how bright it is.
If you go to the eye doctor, they will put liquid drops in your eyes to make your pupils really big, and then they look right through the pupil into the other parts of the eye.
(from: wikipedia - pupil)
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