It’s always fun to try to decipher how an algorithm works. It’s going to be even more fun to write this post without biasing the results: the requirement is to be abstract without being obscure. It seems now that the main page is responding to content, but only that near the top of the page. All linked content pages are still responding as previously described.
This suggests that the top of a page is what’s important, which is an interesting observation, both for those seeking higher placement and for those viewing results. The old adage of "put what you want to say in the introduction" holds true more than ever. I suspect "the top of the page" is the text below the second level header.
If the results no longer trigger off topics related to biochemistry, we’ll know this is true. What’s missing is a way to discover when an indexing event has occurred.