Niddah 8:2-3

Niddah 8:2

A woman may attribute a bloodstain to any probable cause, such as if she slaughtered a domestic or wild animal or a bird, if she was working with bloodstains, or if she sat next to someone else who was working with them. This is also true if she killed a louse. Rabbi Chanina ben Antigonus says she can attribute a stain up to the size of half a split bean to a louse even if she didn’t kill it. A woman may attribute a bloodstain to her son or her husband (if one of them slaughtered an animal, etc.). If she had a wound that could open and bleed, she can attribute the stain to that.

Niddah 8:3

A certain woman once told Rabbi Akiva that she had seen a bloodstain. He asked if she had a wound; she replied that she did but it had healed. He asked if it could still open and bleed and she replied that it could, so he ruled her ritually clean. He saw that his students were confused by this ruling so he asked them why that should be since the Sages declared that we should rule leniently, not stringently. After all, Leviticus 15:19 says, “When a woman has a flow of blood…” – blood, not a bloodstain.