Kim and Amy were fishing a trout stream on a bright afternoon. Both have 20/20 vision. Both are wearing polarized glasses. Kim yelled to Amy, "Hey check out that big fish behind the rock in that run!" But Amy couldn't see it. "No it's right there ..." Kim said. Amy saw nothing, even though she was standing 20 feet from the fish. "Here, I'll show you," said Kim. She made one cast, and caught the fish, right in front of Amy. Why didn't Amy see the fish?