2,116. Causes to Which We Can't Attribute Stains
Hilchos Issurei Biah 9:25
We don’t consider the possibility that blood was moved from one place to another in order to attribute a stain to it. For example, if a woman had a wound on her shoulder and a stain was found on her calf, we don’t hypothesize that she touched the wound with her hand and then touched elsewhere on her body. The same is true in all similar situations; neither stains on her body, nor those on her clothes are attributed to such wounds.
Hilchos Issurei Biah 9:26
Let’s say that two women jointly slaughtered a bird and it only held a volume of blood the size of a sela. If a stain the size of a sela was found on each woman, they are both unclean. If a woman was working with blood that could make a stain no larger than a gris and a stain the size of two gris was found on her, she may attribute one gris to the blood she was working with and the other to a louse. If the stain is any larger than two gris, she is unclean.