Normal sudoku rules apply. The grid is divided into 9 snakes. Each snake is a path of length 9, starting at its tail in the southwest and moving orthogonally north or east — never west or south — to its head in the northeast. Three heads (red diamonds) and two tails (green squares) are shown, pointing to the next cell in that snake. Digits in a snake cannot repeat. The snake that contains the blue dot is a thermosnake, with digits increasing from its tail to its head. Adjacent digits connected by a dot differ by 1 if the dot is white, and have a ratio of 1:2 if the dot is black.