I am surprised no one has brought up http://www.xkcd.com/915/ yet.

(I may one day regret posting this comment, but... when that XKCD was published, I remarked in #lesswrong that it was entirely correct, and pointed to myself: as a result of my years cleaning a dog pen, I had developed distinct aesthetic preferences as far as feces went. They can vary widely in attractiveness based on coloring, water-content, foreign bodies, etc.)