Only just discovered this wonderful trick. Last week I scratched at a scabbed scratch on my arm and of course splattered blood all over my nice pretty green work blouse. Cotton, but not knit. Co-worker suggested the saliva trick. It worked.
Enzymes in your saliva break down the blood.
Today I found blood on the sleeve of another shirt. Cotton jersey fabric. I must have done it again and not realized it. This was dried blood several days old. My saliva took that blood out too.