DOCTOR: As you come into this world, something else is also born. You begin your life, and it begins a journey towards you. It moves slowly, but it never stops. Wherever you go, whatever path you take, it will follow. Never faster, never slower, always coming. You will run. It will walk. You will rest. It will not. One day, you will linger in the same place too long. You will sit too still or sleep too deep, and when, too late, you rise to go, you will notice a second shadow next to yours. Your life will then be over.