Quote from : D'Aulaires' Book of Norse Myths Book

They spell-caught the sounds of cat paws, the breath of fish, the spittle of birds, the hairs of a woman's beard, and the roots of a mountain, and spun them around the sinews of a bear. That made a bond that looked as fine as a ribbon of silk, but, since it was made of things not in this world, it was so strong nothing in the world could break it.