There are many, many more things that nobody knows. Do animals have a sense of humor? Why do we have five fingers? How long can humans live? What did Jesus do in his youth? Which speech did Lincoln deliver at Gettysburg? Does the appendix have any use? Is there an odd perfect number? In this witty and enlightening follow-up to  The Things that Nobody Know s, William Hartston takes us on a guided tour of 501 further gaps in our knowledge of cosmology, mathematics, animal behavior, medical science, music, art, and literature.