You are so young, Lyra, too young to understand this, but I shall tell you anyway, and you'll understand it later: men pass in front of our eyes like butterflies, creatures of a brief season. We love them; they are brave, proud, beautiful, clever; and they die almost at once. They die so soon that our hearts are continually racked with pain. We bear their children, who are witches if they are female, human if not; and then in the blink of an eye they are gone, felled, slain, lost. Our sons, too. When a little boy is growing, he thinks he is immortal. His mother knows he isn't. Each time becomes more painful, until finally your heart is broken. Perhaps that is when Yam be-Akka comes for you. She is older than the tundra. Perhaps, for her, witches' lives are as brief as men's are to us.

The Golden Compass