

Apples and Oranges – A Comparison - percept
http://www.improbable.com/airchives/paperair/volume1/v1i3/air-1-3-apples.html

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Gravityloss
I guess humans (and many other animals, but especially apes) have specifically
evolved to be extremely good at discerning apples and oranges. To an alien
they might look the same color and also taste just the same and have the same
scent.

