פירוש על טהרות 4:3

היו מנקרין בהן – if the weasel cast off the creeping animal or the dog [cast off] the carrion that is in their mouths onto the ground and they would peck at it, there is a place for the defilement and its manner of doubt is ritually impure.

Introduction This mishnah is based on the distinction that we have seen several times already if the source of impurity was moving, and we are not sure if it defiled someone or something, the doubt remains pure. But if the source of impurity was considered to be stationary, the doubt is impure.

A weasel that had in its mouth a [dead] sheretz or a dog that had carrion in its mouth and they passed between clean [persons] or if clean persons passed between them, their condition of doubt is deemed clean, since the uncleanness , had no resting place. A dead sheretz and carrion both defile. But since they were moving by being held by the weasel or dog, the people among whom these things moved are clean.

If they were picking at them while these lay on the ground, and a person stated, "I went to that place but I do not know whether I did or did not touch it," his condition of doubt is deemed unclean, since the uncleanness had a resting place. In case two, the dog or weasel are picking at the sheretz or carrion and dragging them on the ground. Despite the fact that the sources of defilement are indeed moving, the mishnah considers anything on the ground to be stationary. Therefore, they do defile the people who might have walked among them.