It flows thru their veins. It grows out of the follicles on their scalp. It's the color of their eyes, the keratin in their nails, the saliva in their mouth, the mucus in their nose, the cells of their skin. It's what they breathe. It's the tears they shed.
They use it as a clever weapon in communication. It deforms their vision, corrodes their heart and mind, warps their conscience and keeps them staggering thru life.