Here’s a pair of Finnish Snakes. One puzzle’s shaded givens (dark gray cells) are the others’ blank givens (light gray cells), and vice versa (ignoring the head and tail). Sticking to the symmetric layout and duality restrictions probably made both puzzles a little worse than what they could’ve been alone, though. I also couldn’t get the lengths match up.
I was going to use white/black circles instead of coloured cells, but couldn’t bother in the end.
- Shade some cells to form a snake.
- The snake must use all dark gray cells, and none of the light gray cells.
- The head and tail (numbered cells) are given, and indicate the snake’s length (49 and 47 cells long, respectively).
- The snake doesn’t touch itself, even by corners.
EDIT: On the second snake, fixed the clue at R1C5.