Complex sentence: Rincewind is apparently the only wizard who still remembers the Librarian's name, but he has agreed not to tell anyone, possibly because the Librarian is capable of bouncing the head of a man on the pavement when holding him by the ankle.
Split into simpler sentences: Rincewind is apparently the only wizard who still remembers the Librarian's name, but has agreed not to tell anyone. Possibly because the Librarian is capable of bouncing the head of a man on the pavement when holding him by the ankle.