» Blood
Thick blood: Thick blood is gained whenever a Heaven Smile is defeated by shooting its weak spot, or shooting either its head or any of its limbs off. Camellia, Micro and Flower Smiles will give you a fair amount of thick blood once defeated. The maximum amount of blood you can hold is 1000kj. Thick blood is used to create serum via the blood machine (which is accessible at the TV on channel B), to level up the Smith personalities.
» See this section for more info about thick blood in regards to leveling up.
Thin blood: When you kill enemies, you also collect thin blood, which is used to either heal your character, or to use for their special abilities and/or special attacks. In normal mode, you can collect up to 20 vials of thin blood and in Killer 8 (the hardest mode), the max is 5. I've not played Deadly (hard) yet, so I'm not sure what the max is for that mode.