If two siblings are forced by fate to separate, before each goes about their own destined path, they can pierce a tree with their knives. One will plunge their blade toward the east, the other toward the west. In turn, one sibling leaves heading east and the other off towards the west to correspond with the direction of their knives. The knives in the tree become divinatory tools that the siblings, in each other’s absence, can use to check on the well-being of the other. If one of the siblings dies, the blade of their knife will rust and as long as they live the blade will be as new.
P. Herrmann Deutsche Mythologie 1898
J. & W. Grimm Kinder– und Hausmärchen 1812