The Gemara asks: And in what way is uncertainty whether he interrupted the slaughter or pressed the knife different from uncertainty whether the knife became notched before or after the slaughter? The Gemara answers: There, in the case of uncertainty with regard to interruption or pressing, the flaw developed in the animal, and the slaughter is not valid. Here, in the case of uncertainty whether the knife became notched before or after the slaughter, a flaw developed in the knife but a flaw did not develop in the animal, and the slaughter is valid.

And the halakha is in accordance with the opinion of Rav Huna that the slaughter is not valid in a case where he did not break a bone with the knife. And the halakha is in accordance with the opinion of Rav Ḥisda that the slaughter is valid in a case where he broke a bone with the knife. Learn by inference that Rav Ḥisda rules that the slaughter is valid even if he did not break a bone with the knife. The Gemara asks: But if he did not break bones, on what was the knife notched? It must have been on the hide. Why, then, is the slaughter valid? The Gemara answers: Say that it was notched on the neck bone after he competed slaughtering the animal.

The Gemara relates: There was an incident, and Rav Yosef deemed as many as thirteen animals tereifot when he discovered the knife was notched after slaughtering the final animal. The Gemara asks: In accordance with whose opinion did Rav Yosef issue his ruling? Is it in accordance with the opinion of Rav Huna, who holds that the concern is that the knife was notched by the animal’s hide, and he ruled that even the first animal is forbidden? The Gemara answers: No, perhaps it is in accordance with the opinion of Rav Ḥisda, who holds that the notch is attributed to the neck bone, and they are all forbidden except for the first animal.

And if you wish, say instead: Actually, it is in accordance with the opinion of Rav Huna, as, if it were in accordance with the opinion of Rav Ḥisda, since we attribute the notch to the neck bone as a leniency, from where is it ascertained that it is on the neck bone of the first animal that it was notched? Perhaps it is on the neck bone of the last animal that it was notched, and all of the animals are permitted.

Rav Aḥa, son of Rava, said to Rav Ashi: Rav Kahana requires an examination of the knife between each and every act of slaughter. The Gemara asks: In accordance with whose opinion did Rav Kahana issue his ruling? Is it in accordance with the opinion of Rav Huna, and he stated the halakha to invalidate the slaughter of the first animal that he slaughtered if he discovers a notch in the knife? The Gemara answers: No, perhaps it is in accordance with the opinion of Rav Ḥisda, according to the first of the two explanations of the ruling of Rav Yosef, who holds that if a notch is found it is attributed to the neck bone, and examination of the knife is required to validate the slaughter of the next animal.

The Gemara raises an objection: If so, and the reference is to the examination before slaughter, the knife should require the examination of a Torah scholar that was required by the Sages. The Gemara explains: There is no need for a Sage to examine the knife, based on the principle: The testimony of one witness, in this case the slaughterer, is deemed credible with regard to ritual matters. The Gemara challenges: If so, even from the outset, examination of the knife by a Torah scholar should also not be required. The Gemara explains: Didn’t Rabbi Yoḥanan say that the Sages said to show the knife to a Torah scholar only due to the requirement to show deference to the Sage? Once deference was shown before the initial slaughter, it is no longer necessary to do so.

§ Apropos the statement of Rav Huna that an animal during its lifetime exists with the presumptive status of prohibition, and therefore in cases of uncertainty whether the animal was properly slaughtered, one rules stringently and it is prohibited to eat its flesh, the Gemara asks: From where is this matter that the Sages said: Establish the status of the matter on the basis of its presumptive status, derived?

Rabbi Shmuel bar Naḥmani said that Rabbi Yonatan said that the verse states with regard to leprosy of houses that after a priest views a leprous mark: “And the priest shall emerge from the house to the entrance of the house, and quarantine the house seven days” (Leviticus 14:38). The Gemara asks: How can the priest quarantine the house based on his viewing the leprous mark? Perhaps as he was emerging and coming out of the house, the size of the leprous mark diminished and it lacks the requisite measure for leprosy. Rather, is it not due to the fact that we say: Establish the status of the matter on the basis of its presumptive status?

Rav Aḥa bar Ya’akov objects to that proof: And perhaps the verse is referring to a case where the priest emerged backward, as in that case, the priest sees the leprous mark as he emerges.

Abaye said to him that there are two refutations of that statement. One is that emerging backward is not called emerging, and the priest would not fulfill the verse “And the priest shall emerge from the house” by doing so. And furthermore, in a case where the leprous mark is behind the door, what is there to say? Even walking backward would not enable the priest to see it. And if you would say that the priest can open a window in the wall to enable him to see the leprous mark, but didn’t we learn in a mishna (Nega’im 2:3): In a dark house one may not open windows to enable him to see his leprous mark?

Rava said to Abaye: With regard to that which you say: Emerging backward is not called emerging, the case of the High Priest on Yom Kippur will prove that this is not so, as emerging is written in his regard (see Leviticus 16:18), and we learned in a mishna (Yoma 52b): The High Priest emerged and came out backward in the manner of his entry, facing the Ark in the Holy of Holies. And with regard to that which you say: In a dark house, one may not open windows to enable him to see his leprous mark, this statement applies only in a case where the existence of a leprous mark in the house was not yet established; but in a case where the existence of a leprous mark in the house was already established, it was established, and the priest may open a window to view it.

It is taught in a baraita not in accordance with the opinion of Rav Aḥa bar Ya’akov, who suggested that the verse is referring to a case where the priest emerged from the house backward and therefore there is no proof that one lets the matter remain in its presumptive status. It is written: “And the priest shall emerge from the house to the entrance of the house and quarantine the house.” One might have thought that he may go into his own house and quarantine the house from there; therefore, the verse states: “To the entrance of the house,” referring to the house that is being quarantined.

If he must emerge to the entrance of the house, one might have thought that he may stand beneath the lintel and quarantine the house; therefore, the verse states: “From the house,” indicating that he does not quarantine the house until he emerges from the house in its entirety. How so? He stands alongside the lintel and quarantines the house.

The baraita concludes: And from where is it derived that if he went inside his own house and quarantined the leprous house, or that if he stood inside the leprous house and quarantined it, that his quarantine is a valid quarantine? It is derived from that which the verse states: “And quarantine the house,” meaning in any case. Apparently, the quarantine is valid even if he is unable to see the leprous mark, as the mark remains in its previous presumptive status.

And Rav Aḥa bar Ya’akov interprets the baraita in accordance with his opinion