What is higher without the head than with it?

A pillow is higher without the head than with it. This is the answer to a popular modern riddle that is a part of many games and phone applications such as "Guess the Riddle" on iTunes.

Riddles are not particular to any one country or culture, but are found throughout the world. Archaeologists can trace the origin of riddles back thousands of years to places such as China and Japan, where they discovered puzzles etched on the walls of caves and temples. Occasionally these etchings involved mathematical formulas, but many were merely for fun and entertainment. It is thought that strategy board games, such as chess, may have even developed from early riddles.