Katakans and their more dangerous kin, nekurats, are the embodiments of human fear. They hide in the shadows. They feed on blood. They resemble enormous bats — though with long fangs and even longer talons. And, as if that weren't terror enough, they can turn invisible, waiting unseen while dread of their unpreventable attack overwhelms their victim.
- See this subject on The Witcher wiki: Katakan