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A Pinhole Camera Oddity

Position yourself so that one of your eyes is close to a pinhole source of light and carefully place some small object between your eye and the pinhole, say, a pencil. On your retina the object's shadow will will be in your field-of-view from the opposite side from the object's image.
If the object moves into your field of view from below, then its shadow will enter from the top. If the object moves in from the right, it's shadow will come in from the left. (The object's image will be faint and washed out but the shadow will be quite distinct.)

The reason for this unexpected phenomenon is that the shadow is non-inverted on your retina (it is created inside the pinhole camera) and your brain flip-flops all the retinal information including that for the shadow.

Updated 28 September 2002