Conclusion: This shows that we are more stringent about danger than about prohibitions.

(Mishnah): Three liquids are forbidden if they were exposed: water, wine and milk;

If they are exposed for the amount of time it takes for a snake to come from a nearby hiding place and drink, one may not drink them.

Question: What is considered a nearby place?

Answer (R. Yitzchak brei d'Rav Yehudah): It is to come from under the handle of the flask, and drink.

Objection: If they were exposed only for the time to come and drink, if a snake drank, one would still see it (for it had no time to return)!

Correction: Rather, they must be exposed for the time of a snake to come, drink and return to its hole.

(Rav Huna): If after Shechitah, a nick was found in the knife, even if the knife was used to break bones the entire day (after the Shechitah, before it was checked), the Shechitah is invalid. We are concerned lest the nick came when the knife cut the animal's skin, before cutting the Simanim;

(Rav Chisda): The animal is permitted. We assume that the nick came when cutting a bone.

Question: Granted, Rav Huna holds like he taught;

(Rav Huna): An animal is forbidden (to eat) when it is alive. After death, we assume that it is still forbidden unless we know that it was slaughtered properly.

However, what is Rav Chisda's reason?

Answer: A bone certainly can cause a nick. Perhaps the skin can. We attribute (the nick) to something certain, and not to something doubtful.

Question (Rava - Beraisa): A Tamei man immersed, and later found a Chatzitzah (obstruction) on his body. Even if he was working the whole day (after immersing) with the substance he found on his body, the Tevilah does not count, unless he is sure that there was no Chatzitzah when he immersed;

Here, he certainly immersed, and we are unsure if there was a Chatzitzah, and we assume that what is doubtful occurred!

Answer: That case is different. We know that the man was Tamei. We leave him in his status quo.

Question: Here also, the animal was forbidden before Shechitah. We should leave it in its status quo, and say that it was not slaughtered!

Answer: You cannot say that. It is slaughtered in front of us!

Question: Also here, the man immersed in front of us!

Answer: Regarding the man, something (the Chatzitzah) suggests that the Tevilah was invalid.

Question: Also regarding Shechitah, the blemish on the knife suggests that the Shechitah was invalid!

Answer: There, the blemish is not on the party in question (the animal itself). Regarding Tevilah, the blockage is on the man himself.

Question (against Rav Chisda - Beraisa): If one slaughtered the Vesht, and then the Kaneh was uprooted, it is Kosher. If the Kaneh was uprooted before cutting the Vesht, it is invalid;

If one found the Kaneh uprooted, and does not know whether this happened before or after cutting the Vesht, any Safek Shechitah is invalid.

Question: What do the words 'any Safek Shechitah is invalid' come to include?

Suggestion: They include our case (that Rav Huna and Rav Chisda argue about).

Answer: No, they include when we are unsure whether he paused or pressed during the Shechitah.

Question: Why is that invalid, but (according to Rav Chisda) our case is not?

Answer: There, there was a problem in the animal itself. In our case, there is not. (The problem is only in the knife.)

The Halachah follows Rav Huna when the knife was not used to cut bones afterwards. The Halachah follows Rav Chisda when the knife was used to cut bones afterwards.

Question: Since we needed to say that the Halachah follows Rav Huna when the knife was not used to cut bones afterwards, this implies that Rav Chisda argues. To what does he attribute the blemish in the knife?

Answer: It became blemished through the neckbone.

A case occurred in which Rav Yosef forbade 13 animals due to a blemish found in the knife after they were all slaughtered.

Suggestion: This must be like Rav Huna. Also the first animal was forbidden.

Opinion #1 - Rejection: It can be even like Rav Chisda. The first animal was permitted, and the rest were forbidden.

Opinion #2: Indeed, it must be like Rav Huna;

Rav Chisda is lenient to say that the knife became blemished on the neckbone. If so he should be lenient also to say that it became blemished on the neckbone of the last animal, and permit all of them!

Rav Kahana required butchers to check their knives after every Shechitah.

Suggestion: He holds like Rav Huna. If a blemish is found, this disqualifies the previous Shechitah.

Rejection: No, he can hold like Rav Chisda. Even if a blemish is found, we attribute it to the neckbone. The Shechitah was Kosher;

The knife must be checked to avoid invalid Shechitah of subsequent animals.

Question: If so, (we check afterwards for the sake of subsequent Shechitos), we should require a Chacham to check the knife (just like a Chacham must check it before Shechitah)!

Answer: One witness is believed to testify about what is permitted and forbidden. (We trust the butcher to say that he checked it.)

Question: If so, similarly, we should not require a Chacham to check the knife before Shechitah!

Answer: Correct! R. Yochanan taught that the only reason we require the Chacham to check the knife is for the honor of the Chacham.

Question: Chachamim say that when in doubt, we follow Chazakah (the status quo). What is the source for this?

Answer (R. Yochanan): "The Kohen will leave the house (with Tzara'as), to the entrance. He will close (quarantine) the house for seven days."

Question: Perhaps when he left, the plague got smaller, and it is now smaller than the size needed to quarantine a house!

Answer: We rely on Chazakah, and assume that the plague is still large enough!

Question (Rav Acha bar Yakov): Perhaps the Kohen exited the house walking backwards, and saw the plague the whole time!

Answer #1 (Abaye): It says "he will leave the house." Walking backwards is not called 'leaving'.

Answer #2 (Abaye): If the plague is in back of the door, in any case he cannot see it after exiting!

Question: Perhaps he makes an opening in the door to see the plague.

Answer (Mishnah): We do not make a window in a dark house to enable the Kohen to see the plague. (The same applies here.)

Objection (Rava - to Answer #1): It says "(the Kohen Gadol) leaves (the Kodesh ha'Kadoshim)", and a Mishnah says that he exits the way he entered. This shows that walking backwards is called 'leaving'!

Objection (Rava - to Answer #2): Perhaps we do not make an opening to see if a discoloration in the wall is truly a plague, but once a plague was seen, we make a window to see if it is still the proper size!

Question (against Rav Acha bar Yakov - Beraisa) Suggestion: Perhaps "the Kohen will leave the house" teaches that he returns to his own house, (and later returns,) and closes (the house)!

Rejection: It says "to the entrance";

Suggestion: Perhaps "to the entrance" teaches that he stands in the doorway and closes!

Rejection: "From the house" teaches that he fully leaves the house.

To fulfill both, he stands outside the doorway and closes it.

"And he will close the house" teaches that even if he returned to his own house and closed, or closed it from inside the plagued house, it is quarantined. (Even though he cannot see the plague from his own house, he may assume it still has the required size, unlike Rav Acha!)

Answer: The case is, there is a line of people from plagued house to the Kohen's house, and they tell him that the plague still has the required size.