A lighted-hearted scientific look at the rituals and icons of Christmas. How does snow form? Why are we always depressed after Christmas? How does Santa manage to deliver all those presents in one night? (He has, in fact, little over two ten-thousandths of a second to get between each of the 842 million households he must visit.) This book contains information on how drugs might make us see flying reindeer, how pollution is affecting the shape of Christmas trees and the intriguing correlation between the length of our Christmas card list and brain size.