Via Daily Nous, I came across a free set of text analysis tools by Voyant. You can paste in a passage or point it at some URLs, and it will chop it into words and phrases.
I let it chew on my book, and one of the products was this graph of word density:
It looks all sciencey, like the kind of think that prop people might put on a screen in the background of a lab scene. It isn’t very informative, though. The curve has “species” dipping below zero, even though it occurs at least once in every segment.
I learned that “natural”, “kind”, and “kinds” make up about three percent of the words in the book. That three percent was, I suppose, the easiest part to write.