Normal sudoku rules apply. Draw a snake in the grid that starts and ends in the cells with the circles. The snake wriggles horizontally and vertically and never touches itself, not even diagonally. The digits on the snake form a palindrome ie they read backwards the same as forwards. The digits in grey cells are not part of the snake and indicate how many of the horizontally, vertically and diagonally adjacent cells are part of the snake. All possible grey cells are given.