saliva works because it has enzymes in it that begin the digestive process, and break it down. it goes for the cellular structure, and will loosen the blood, but if it stays there long enough, it will still stain fabric. blood has an iron content. when it is exposed to oxygen, it begins to oxidize, creating, effectively, rust. but yup. spit as a frist line of defense is best! just be sure it is your own blood if there is any kind of chance of contamination. somebody else's blood is considered to be hazardous waste!