And it is taught with regard to that halakha in the mishna that Rabbi Yosei deems it pure. To which halakha in the mishna is this referring? If we say that it is referring to the latter clause of the mishna, which discusses a chest placed in the entrance of the house, the first tanna also deems it pure in that case.

Rather, it is clear that the first tanna says that if a source of impurity is inside the compartment of a chest that is inside the house, the house is impure, either because it is typical for a source of impurity to exit its location, or because he holds that a hidden source of impurity breaks through and ascends. And Rabbi Yosei disagrees and says to him: With regard to that which you say that it is typical for a source of impurity to exit its location, it is not necessarily so. One can remove the impure item in halves or burn it in its place inside the compartment. And with regard to that which you say that a hidden source of impurity breaks through and ascends, a hidden source of impurity does not break through. Consequently, Rabbi Yosei must hold that a hidden source of impurity does not break through and ascend.

§Based on the previous statement of Rabbi Yosei, the Gemara established that Rabbi Yosei holds that a hidden source of impurity does not break through and ascend. And the Gemara raises a contradiction between that previous statement of Rabbi Yosei and another statement of Rabbi Yosei.

As we learned in a mishna (Oholot 11:7): In the case of a dog that ate the flesh of a corpse, and the dog then died and is lying on the threshold in such a manner that its neck and mouth are facing toward the inside of the house, Rabbi Meir says: If there is an opening the size of one cubic handbreadth inside the neck of the dog, i.e., the neck itself constitutes this measure, the dog imports impurity into the house because the upper portion of the dog’s body overlies the impure item inside the dog and the impurity is transmitted through the neck and mouth of the dog into the house. But if there is not such a large cavity in the neck of the dog, then there is no halakha of a tent, and the dog does not import the impurity into the house.

Rabbi Yosei says: One looks to determine exactly where on the threshold the dog is located. If the impure item inside the dog is located anywhere from opposite, i.e., under, the lintel and toward the inside of the house, the house is impure. If the dog is located anywhere from opposite the lintel and toward the outside of the house, the house remains pure.

Rabbi Elazar says: One must determine the exact manner in which the dog is lying on the threshold. If its mouth is located inside the house, but its rear is located outside the house, the house remains pure. If its mouth is located outside the house but its rear is located inside the house, the house is impure. This is because the source of impurity exits the dog’s body through its edge, i.e., its rear.

Rabbi Yehuda ben Beteira says: In both this case and that case, i.e., whether the dog is lying such that its mouth is inside the house or outside the house, the house is impure. The reason is that the impure item can exit through either the mouth or the rear.

The Gemara analyzes the statement of Rabbi Yosei that if the dog is located anywhere from under the lintel and toward the inside of the house, the house is impure. What, is the statement of Rabbi Yosei not referring to a case where there is not an opening the size of one cubic handbreadth inside the dog’s neck, with regard to which Rabbi Meir says that the house remains pure? Accordingly, Rabbi Yosei is responding to Rabbi Meir and saying: Even if the neck of the dog is not the size of one cubic handbreadth, as long as the impure item inside the dog is located from under the lintel and toward the house, the house is impure because it overlies the impure item.

And therefore learn from it that Rabbi Yosei holds that a hidden source of impurity breaks through and ascends, contrary to Rabbi Yosei’s opinion as understood from his previous statement.

Rava said: Rabbi Yosei holds that a hidden source of impurity does not break through and ascend. As for that which Rabbi Yosei teaches: One looks whether the impure item inside the dog is located opposite the lintel and toward the inside of the house, Rabbi Yosei actually teaches: One looks at the empty space adjacent to the source of impurity. And Rabbi Yosei disagrees with Rabbi Meir with regard to two matters, and says to Rabbi Meir: As for that which you say that if there is the width of one cubic handbreadth in the neck of the dog, it imports the impurity into the house, that is not so. Rather, we follow the measure of the empty space, i.e., the neck of the dog imports impurity into the house only if it contains a cubic handbreadth of space in addition to the thickness of the flesh of the neck itself.

And with regard to that which you say that even if the dog is located on the outer portion of the threshold of the house, the entire house is impure, that is not so. Rather, if the impurity inside the dog is located anywhere from opposite the lintel and toward the inside of the house, the house is impure. If the impurity inside the dog is located anywhere from opposite the lintel and toward the outside of the house, the house remains pure.

Rav Aḥa, son of Rava, teaches that Rava’s explanation is explicit in the mishna itself, as follows: Rabbi Yosei says: One looks at the empty space adjacent to the source of impurity.

§Previously the Gemara established that Rabbi Yosei holds that with regard to the halakhot of impurity, overlying is referred to as touching, as the transmission of impurity via contact and via overlying are considered one category. But the mishna (Oholot 3:1) cited earlier (125b) states that in the case of one who touches half an olive-bulk of flesh of a corpse, if a tent simultaneously overlies him and another half an olive-bulk of flesh he remains pure. Evidently, there is a tanna who disagrees with Rabbi Yosei and holds that these two methods of transmitting impurity are not the same category. The Gemara asks: Who is the tanna who disagrees with Rabbi Yosei? The Gemara answers: It is Rabbi Shimon, as it is taught in a baraita: Rabbi Shimon says: