There are many, many more things that nobody knows...Why do we have five fingers? Do animals have a sense of humour? Did the universe have a beginning? What causes deja vu? Why do cats purr? How fast did dinosaurs move? From the trivial to the profound, William Hartston reveals 501 further gaps in our knowledge of our planet, its history and culture and the universe beyond - never has ignorance been so enlightening and entertaining.