|Count the number of Chinamen on the world.|
|Click here to rotate the Earth.|
How do you explain it?
If you cut out the central portion of this figure along the world-edge, then shift the arrow to point to N.W. instead of N.E., you will discover that you have one less figure than before. This is Sam Loyd's famous Vanishing Chinaman Effect, probably the most famous puzzle of its sort. (From Mathematics, Magic and Mystery by Gardner.)