[ceptimus]

In Pullman's His Dark Materials trilogy, the subtle knife is a man-made tool that can create either by accident or design, 'Specters'.

Specters are described as 'creatures of pure amoral evil' and 'children of the abyss'. Specters feed on the souls or dæmons of people, leaving them soulless zombies. However these dæmonless people are not infectious to others - they are merely the objects of great pity and the cause of immense sadness.