I tried my experiment suggested here to look for something with no assigned category. I was driving along Arden Way happily categorizing everything when I came upon a group of useless green columns. ?? My mind immediately set to work processing the surroundings and quickly came up with: commercial art objects. That's all I've been able to find so far that caused even a split second hesitation in the constant process of classifying everything.
Computers don't do this. They successfully categorize precisely those things you tell them to and not one damn other thing. Believe me, I know.