Normal sudoku rules apply. Additionally the solver must find a single snake of orthogonally connected digits beginning at the given 1 which does not touch itself (even diagonally), does not touch any white dots but must visit each 3x3 box in the grid. Each digit on the snake is the sum of the previous two digits modulo 10 (eg 5+7 = 2). NB The second snake digit after the given 1 can be any digit. Grey digits are not on the snake but show the number of snake cells in the surrounding (up to) eight cells. Cells separated by a white dot must contain consecutive digits. Not all possible dots are given.