Remarkable book. What I find as remarkable is that it has been translated! That must have been hard. (In the German edition, this puzzle, btw, features S,T,H,M and A-A.)
I think 'asthma' would work as an answer then. I've only read the English version so I don't know, but was wondering if the 'degenerate' case also comes up in the German version.
Yes, Achilles complains about the turtle's 'degenerate' answer, which would have to have been 'A'. Not really a word in German. Wonder whether there could have been a better equivalent, but presumably the translator spent some time on it. I don't have a German dictionary on hand to try the trick in the article.