What’s the frequency, Ngram Viewer?

The Google Books Ngram Viewer may not be remembered as one of the 21st Century’s most useful (or statistically sophisticated) inventions, but the patterns revealed in its phrase-frequency charts can be addictively entertaining. For example:

— Tar Heel vs. Tarheel

— beef barbecue vs. pork barbecue

— North Carolina football vs. North Carolina basketball

— University of North Carolina vs. Duke University

— Research Triangle vs. Bermuda Triangle and isosceles triangle