Normal sudoku rules apply. Digits separated by a white dot must be consecutive. Digits separated by a black dot must have a ratio of 1:2. A fly has flown across the page, in orthogonal lines. It always went north from a cell containing a 2, east from a 4, south from a 6, and west from an 8. On odd digits, it kept going in a straight line. The fly entered the grid heading west at the arrow, and exited heading east at the bottom right of the grid. It did not leave and re-enter the grid at any point. The fly may have crossed its own path, but it never flew directly across a dot.