Henry Ernest Dudeney/Modern Puzzles/220 - The Fly's Tour

by : $220$

 * The Fly's Tour
 * I had a ribbon of paper, divided into squares on each side.
 * I joined the ends together to make a ring, and tossed it down onto the table.
 * Then I watched a fly land on the ring and walk in a line over every one of those squares on both sides,
 * returning to the point where it started, without ever passing over the edge of the paper.
 * Its course passed through the centre of the squares all the time.


 * How was this possible?