Thanks, Michael.
Unfortunately, this does not help in this case.
I have found a number of variants to the initial string which triggers the 403. Some of those which do trigger it pass the whyspam test. The original phrase and some more which also trigger the 403 in my pages also trigger the 403 for the whyspam test instead of telling me the rules that fired for doing so.
It now appears that any phrase starting with 'having', followed by one or two spaces, followed by an arbitrary sequence of letters (perhaps other things, too, didn't really test that much), optionally followed by spaces, followed by an interpunction mark will raise the 403 (both in a page and in whyspam).
I also seem to have found a workaround. adding several spaces between having and the succeeding word seems to be acceptable to the gremlins that be.