Normal sudoku rules apply. Connect each pair of matching coloured spots with a snake. Snakes may only move orthogonally through the grid, not diagonally. They may touch each other (and themselves) but cannot share cells. Each pair of adjacent digits along a snake has the same difference, but this 'difference value' may be different for different snakes. A grey square contains an even digit. A black dot connects two digits with a 1:2 ratio (one is double the other.)