Correlation ≠ Causation

A cautionary note sounded in every statistical analysis course, but what does it mean? I offer this email sent to Kerry from Amazon.com:

Dear Amazon.com Customer,

We've noticed that customers who have purchased "The Sandman Vol. 8: Worlds' End" by Neil Gaiman also purchased books by B. G. Pachpatte. For this reason, you might like to know that B. G. Pachpatte's "Integral and Finite Difference Inequalities and Applications, Volume 205 (North-Holland Mathematics Studies)" will be released soon.

And lest you think that "Integral and Finite Difference Inequalities and Applications, Volume 205" is an ironic name for some edgy new graphic novel, it's not. From the Amazon description: "The monograph is written with a view to provide basic tools for researchers working in Mathematical Analysis and Applications, concentrating on differential, integral and finite difference equations. It contains many inequalities which have only recently appeared in the literature... Will be of interest to researchers working both in pure and applied mathematics and other areas of science and technology, and it could also be used as a text for an advanced graduate course." And, apparently, will be of interest to readers of quality fantasy and/or comics.