I'd use the audio option in the reCraptcha and then see how little of what I heard I could get away with actually entering into the form. Often it sufficed to just type one word out of the entire audio clip or even enter a word which sounded similar [eg. audio clip says "tranced", I write "transit"]. The most satisfying ones of all where when, after listening to a complete sentence containing either word, I could pass the reCraptcha by simply typing "the" or "an" into the form.
One of the things that I find slightly disappointing about Buster is that it types in the entire sentence, when solving the reCraptcha. I hate to think Google are under the impression I've suddenly started trying harder!
Granted this is mostly a kerning issue.
Without wider textual context the correct answer is hard to determine.
I like to think that somewhere out there on Google Books, my efforts have resulted in an innocuous word being replaced with something offensive.