My latest book in hardbound (in paperback as of October, 1997), Astronauts is the first book since Why Do Clocks Run Clockwise? not to pose new Frustables? (Why? The next book of Imponderables, when it comes out, will recapitulate all 80 of the original Frustables).
 
Astronauts also introduces the first-ever Imponderables Contest, the winners of which will be announced when Imponderables X is released.
 
Some of my favorite Imponderables from this book: How do they keep more than two pieces of a jigsaw puzzle from fitting together? How do they keep soda in soft-drink machines from freezing in the winter? Why don't women pole-vault? And why do bombs create mushroom-shaped clouds?
 
Want to see a few samples from the book?
 
Sample 1 -- Why do ceiling fan blades get dusty, despite constantly spinning?
Sample 2 -- Why did Pirates wear earrings?