Hidden information in page 307-308 of many books: a key left by editors who are hiding biochemical "needles in haystacks"

I noticed last year that pages 307-308 of many books contain on one page of the pair of pages some imagery--either actual illustrations or written descriptions--resembling an erupting volcano. These pairs of pages then contain words on the different pages that often relate to research I've been doing on nutrition and other ways in which chemistry and physics interact with the human body. The word pairs include dyads like kelp:fur, clanging bells:lulling music, rings:magic, etc. It rather reminds me of the analogy section of the old SAT exams.

I think that some editors intentionally have been hiding important biochemistry-related information and left this pattern as a "key" in older books (newer ones often lack the same pattern, and self-published books for small readership never seem to contain it) to identify themselves to each other. My library is limited. I can only imagine how much information could be found in larger collections of older books, though, using this key.