- ➊ Write into some white cells numbers between 1 and 5 so that one or more sequences of orthogonally adjacent cells are built, containing all numbers in strictly increasing or decreasing order (number snakes).
- ➋ Two number snakes may not touch orthogonally (diagonally is allowed).
- ➌ A Number in a black cell indicates which number in a white cell is the first number in the direction the arrow points to. This number must not be directly adjacent to the black cell; there may be empty white cells in between. A zero denotes that there is no number cell in the direction the arrow points to.
- ➍ No snake may see another snake. A snake's eyes are on the side of its head (the 1-cell) opposite the 2-cell. It can only see in that direction, in a straight line, up to the edge of the grid or the nearest black cell (whichever is closer).