Based on your responses, I have just a couple more questions:
> You should use only plurals in your keywords, because a
> search for "apple" will find "apples", whereas a search
> for "apples" will only find "apples," not "apple."
What about plurals in phrases? For example, will a search for "hydrant" match the keyword "fire hydrants"?
Does this only apply to the addition of "s" to a word? It seems to me that the SE's would yield wildly inaccurate results if they searched for any sub-string within the keyword text. For example, in "fire hydrants", one can find the words "ire" and "rant", although those words have nothing to do with fire hydrants. Which leads me into the next question...
>> 3. Word stems. Do the search engines count word
>> stems when counting for spam? For example, would the
>> words 'fish, fishing, fisherman' count as three instances
>> of 'fish'?
> Yes, that would be three instances of "fish." Try to
> always use the longest form of a word. "Fishing" will
> come up in searches for both "fishing" and "fish."
This implies that the SE's look for "words within words". Do they only look for sub-strings from your keyword list (e.g., the word "fish" in the above example), or will any English word match? For example, would the keywords "fish, fishing, fisherman" count as 3x"fish", 1x"is", 1x"in", 1x"her", 1x"ma", 1x"man" (assuming common words are not thrown out). If so, it seems that one could get into spammers-hot-water without even realizing it.