The irresistible epistemology of the visual false negative.

This is one photograph of a spore print, taken of mushroom specimens left for hours on a sheet of black paper and a sheet of white paper:

See the haze of white spores on the black paper? If you think about it, you know that there must be similar patterns of spores on the white paper, too, even though you can't see them. And really, even though you know they must be there, you can clearly see that there's nothing there.