If ever you arrive in our country, and if ever you happen to meet one of the old sisters, you will be asked to deliver me from one sister to another. The distances between the sisters are vast, but take heart. When you become weary, simply rustle my paper, and you will get your strength back.
Of course, you will want to know what I contain, but what ancient sisters have to say to one another over such great distances is a secret that only the sisters know.
The Rustling Letter in The Sister of the Sun, Brown Fairy Book