From Warhammer 40k - Lexicanum
Vapour Rats are mutated vermin, that appear almost skinless, with their wet flesh blending with their surroundings unnaturally.
They are solitary scavengers and carrion eaters and the taste of blood drives them to a feeding frenzy, often drawing them to cannibalism.
- 1: Dark Heresy: Edge of Darkness, pg. 42