Every morning in Tamil Nadu, women draw a kolam on the doorstep with rice flour: a grid of dots, then a line that loops around them. In the sikku kolam the line never ends: one unbroken loop goes around every dot and comes back to where it began. Pick a grid, and the page finds such a line for you. Then watch it being drawn.
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The address of the page keeps this kolam, to share it.
Dots
Line
Look
How the line is made
Halfway between two neighboring dots, the line either crosses itself or turns back, as if it bounced off a little mirror. On the border it always turns back. Follow it from anywhere and it loops around dot after dot until it comes home. Mathematicians call these mirror curves; Paulus Gerdes found the same drawings in the sona sand drawings of Angola.
Finding a single line
With no mirrors, a square of 7 by 7 dots holds 7 separate lines. A mirror where two different lines cross joins them into one. Where a line crosses itself, one mirror keeps it whole and the other cuts it in two. So the page adds mirrors in random order, keeps only those that never cut, and stops when one line is left. Click any point between two dots to try it yourself.