Eric “Needles” from swordandstitchery.com is obviously not done with books yet.
He already came up with the idea of binding guardian spirits into bookplates and it seems he was not yet finished then. One of his recent articles features guiding spirits bound into bookmark guides. Just as little non-native-speaking me was starting to wonder what for Earl´s sake a “bookmark guide” is, the question was answered by one of the pictures in his article showing an oldfashioned German “Lesezeichen” and suddenly my vocabulary was increased by another word.
Of course, this would not be one of Eric´s articles if their would not be a list with random examples of what kind of “teacher” could be found bound into one of such. So, if you would like some inspiration for your gaming table at home for something that make the next spellbook your players pick up a little different… get inspired by Eric himself, hit the link above, break out the dice and let it flow from there.