枕头之谜：人类为何使用枕头？

What leads humans to use pillows and when did we come up with the idea? Pillow talk What is it about the human physiology that leads us to use pillows, and does anyone know when we first came up with the idea? Paul Bethel, London, UK Water world If all the water on Earth’s surface and in the air were put into a ball, how large would the sphere be? Could it exist in space by itself? Pat French Longdon upon Tern, Shropshire, UK Were you able to accumulate all of Earth’s water – ice, liquid and vapour, plus all the water physically and chemically combined with mineral and organic substances – you might reach 1.4 billion cubic kilometres. …