Normal sudoku rules apply. Blue lines are ‘region sum lines’ ie 3x3 box borders divide each blue line into segments with the same sum. Brown lines are ‘product sum lines’ ie the digits on each end of the line must multiply together to give the sum of ALL digits on the line. Draw a 1-cell-wide snake which moves orthogonally and does not touch itself (even diagonally). The snake must enter every 3x3 box exactly once and may not include any cell which is on a line (but may include circled cells). The snake acts as both a region sum line and a product sum line. A digit in a circle indicates the number of times that digit appears on the snake.