What is the reason of the first tanna for declaring that in all uncertain cases of floating impurity the person or item remains pure? Rabbi Yitzḥak bar Avudimi says: In the passage dealing with the impurity of creeping animals and the prohibition of eating them it is written: “With any swarming thing that swarms” (Leviticus 11:43), indicating that a carcass of a creeping animal renders items impure in any place where it swarms. And it is written: “All swarming things that swarm upon the earth” (Leviticus 11:42), indicating that it transmits impurity only if it is on the earth. How so? How can one reconcile these two verses? Definite contact with it renders one impure; one who has uncertain contact with it, e.g., the impurity is floating, remains pure.

The Gemara asks: And Rabbi Shimon, what is the reason for his opinion? Ulla said that as it is written: “Nevertheless a fountain or a cistern in which there is a gathering of water shall be pure” (Leviticus 11:36), this indicates that a creeping animal found in one of these places does not impart impurity. And it is written in the same verse: “He who touches their carcass shall be impure until evening,” which indicates that it does render one impure. How so? If the impurity was floating in water contained in vessels, the item it touched is rendered impure, but if the water was in the ground itself, e.g., in a spring or pit, the item it touched is pure.

The Sages taught (Tosefta, Teharot 3:13): All items that impart impurity that are carried by human hand or that are dragged along are not considered floating impurities, despite the fact that they are in motion. Rather, in a case where there is uncertainty whether a carried or dragged item affected a person, the individual is rendered impure, because the items are considered as though they were at rest. And in the case of items that are thrown by people, in uncertain cases that pertain to them, the individual remains pure.

This is the halakha, except for an olive-bulk from a corpse, which transmits impurity through uncertain contact even if it was thrown; and that which overlies impurity when thrown, i.e., an item that might have been positioned over a corpse when it was thrown; and anything that renders items above it impure like it renders those below it impure. To what does this last clause refer? It comes to include a zav and a zava, who render items placed above and below them impure even without contact. If something thrown or floating might have come into contact with a zav or zava, it is impure.

With regard to this halakha of a floating impurity, Rami bar Ḥama raises a dilemma: If there is a corpse in a vessel and the vessel is floating on water, and one did not overlie it but might have touched it, what is the halakha? Do we go according to the floating vessel or do we go according to the corpse, which is resting on a solid surface?

If you say that we go according to the vessel and one is rendered ritually impure, the following question arises: If a corpse is placed on top of the carcass of a creeping animal, which is floating on water, what is the halakha? Do we say that since this impurity of a creeping animal is an impurity for an evening, i.e., it lasts one day, and this impurity imparted by a corpse is an impurity for seven days, it is considered as though the impurity imparted by a corpse were placed in a vessel, and he is impure? Or, perhaps the fact that both a corpse and a creeping animal impart impurity means that it is one solid impurity, and because the creeping animal is floating he is pure.

And if you say that due to their different levels of impurity it is considered as though the impurity were placed in a vessel and therefore one is definitely impure, one can raise an additional dilemma. If a creeping animal is atop an unslaughtered animal carcass and the animal carcass is floating, then what is the halakha? Do we say that since they are both examples of an impurity for an evening, it is considered a single solid impurity, or perhaps here too they are different, as this one, the carcass, renders items impure when it is the amount of an olive-bulk, and this one, the creeping animal, does so when it is the amount of a lentil-bulk. In that case, the animal carcass and the creeping animal should be considered separate items, and it is as though the impurity is placed in a vessel, and he is impure.

If in that case they are considered separate, then one can also ask: If a creeping animal is positioned atop another creeping animal, what is the halakha? Do we say that these certainly have the same measurement with regard to transmitting impurity, and that they consequently should be viewed as a single floating items, which means he is pure? Or, perhaps, since they are separate from each other and are not in fact a single item, they are not considered as one unit.

And if you say that in the case of a creeping animal atop a creeping animal, since they are separate from each other, it is considered as though the impurity were placed in a vessel and is not floating, one can raise an additional dilemma. If a creeping animal was placed atop an animal carcass that has dissolved, what is the halakha? Do we say that since it has dissolved it has become like liquid, and therefore it is as though the creeping animal were floating on liquid? Or, perhaps this carcass is still considered food, rather than a liquid, and the creeping animal is on a solid surface.

And if you say that a dissolved animal carcasses is considered food, one can raise an additional dilemma. If a creeping animal was placed on top of semen, which is certainly liquid, what is the halakha? Is this creeping animal considered a floating impurity? And if you say that once semen is ejaculated from the body it is considered like food rather than drink, as it is viscous, one can raise an additional dilemma. If a creeping animal was placed atop waters of purification, i.e., the water into which the ashes of the red heifer are mixed, which becomes highly viscous, and the waters of purification are floating on water, what is the halakha? The Gemara responds: We do not know the answer to any of these questions, and therefore the dilemmas shall stand unresolved.