The dragon curve is a single line. It can be drawn with a pencil without 
lifting the pencil and never crossing a line. The dragon curve can be 
generated physically by repeatedly folding a peice of paper and partially 
unfolding it so that each crease is 90 degrees. Its useful as a pattern to 
test graphic plotters because the pen is never lifted during a draw. The 
human being has the amazing ability to recognize any anomoly in a complex 
pattern of half a million vectors, making it a good subject for testing the 
plotter. Ny hickup in the pattern draw will be quickly recognized. 
It also makes a neat screen saver.