We have already learned about the Rabbinic ruling that a woman who finds a ketem on her clothing must behave as if she is a nidda even though on a Biblical level she is not rendered a nidda unless she experienced an actual flow of blood that is accompanied by a physical sensation ( daf 53).
The Mishna on today’s daf teaches that since the rule of a ketem is rabbinic in its origin, if there is any other way to explain the bloodstain, the woman will remain in a state of ritual purity. Thus, if the woman was in a place where there was blood from slaughtered animals, or if she killed an insect or if her husband or son had been bleeding, we do not attribute the stain to menstruation and she remains pure.
The Mishna relates:
A woman once came to Rabbi Akiva and said to him: ‘I have observed a bloodstain.’ ‘Had you perhaps,’ he said to her, ‘a wound?’ ‘Yes,’ she replied, ‘but it has healed.’ ‘Is it possible,’ he again asked her, ‘that it could open again and bleed?’ ‘Yes,’ she replied; and Rabbi Akiva declared her clean. Observing that his disciples looked at each other in astonishment he said to them, ‘why do you find this difficult, seeing that the Sages did not lay down the rule in order to impose restrictions but rather to relax them. ’
It is ordinarily the responsibility of the Sage sitting in judgment to ascertain the truth of a given matter. If the petitioner raises points that will lead to a lenient judgment they will be taken into consideration by the judge, but the judge will not make suggestions that will lead to such a conclusion. Rabbi Akiva’s students were surprised that he openly led the woman in a direction that brought her to make statements that would lead to a lenient ruling. His explanation was that since the laws of ketem are rabbinic in origin, it is reasonable to find ways for leniencies regarding them.