Draw four 3x3 boxes in the grid that don't overlap, and fill them with the digits 1-9. Digits can't repeat in a row, column or 3x3 box. Cells that are not in any box are empty, and their value is 0. Digits can't repeat in a cage, and sum to the clue given in the top-leftmost cell of that cage. Draw four snakes, each existing completely inside one of the 3x3 boxes. Each snake is a one cell wide path that only moves orthogonally, and must pass through every cell of its box. Adjacent digits along a snake sum to 10 or 11.