Most entries for the Book of Fables will unlock while progressing as long as you use or look at every hot-spot. For the last entry, you must replay the last chapter in the Trip Trap bar or choose differently in another playthrough. When you have the choice to tear Grendel's arm off, choose the other action the second time. Tearing his arm off will unlock "Bigby's Vengeance", and leaving the arm intact will unlock "Bigby's Mercy". The "Bluebeard's Fable" entry can also be missed. The first chance to unlock it is in your apartment. It is the file to the left of "Chinese food". Other chances for it will appear when you talk about Bluebeard.