Page and figure references are from the English Penguin Books edition, unless otherwise noted.
What could be the cause of Bach's death? (Sadly, explicitly answered in Chapter IV, p. 86 :-)
What is the translation of si paullum a summo ciscessit, vergit ad imum , in the quoted text from Farkas Bolyai? (p. 92)
Couldn't Fig. 22 (Escher's Relativity) also be seen as an illustration of the possible existence of different worlds with completely different mathematical and logical systems? Every person in the picture lives in his own world, unaware of the others. On a local plane, his world is consistent, but viewed from outside the systems contradict each other. I find Hofstadter's interpretation (p. 97) of the picture a little far-fetched. The relation with the discussion on p. 99 in my opinion is stronger.