|This article is about an older version of DF.|
The favoured drink of Armok, blood (or ichor, for those less-than-favored creatures) is found in most of the creatures in Dwarf Fortress, with the notable exception of skeletal creatures. Blood is not a fluid like water or magma - it is something that is only seen as a stain on creatures, items and the landscape after an injury. If badly wounded, a creature may bleed, and creatures have a limited amount of blood. After enough bleeding, the creature will die.
It comes in several colors, red for most animals and creatures, and aqua/teal for trolls. This stuff usually ends up covering anybody and anything involved in melee combat, especially dogs, cats and wrestlers who must physically be on their target to dispatch them. The blood covering on armor and weapons will inflate creature inventory screens very quickly. A dwarf with the cleaning labor enabled will clean terrain, but there is no (known) negative effect, so it's generally ignored. You cannot currently clean blood from an item or creature, but it will (eventually) wear off.
Blood does not spread. Due to serious problems with it, Toady One has disabled mud/blood spreading for the time being.