A. Said R. Ashi. “Come and take note: A pitcher [of water of purification] that he left uncovered and he came and found it covered — it is unclean [cf. M. Parah 11:1].” For I may say that an unclean person came in there and covered it up. But if he left it covered and came in and found it uncovered — if a weasel could drink from it, or [if] a serpent [could drink from it] according to R. Gamaliel, or if dew could have fallen in it at night — it is unfit [for use as purification water, but it is not deemed unclean].
B. And said R. Joshua b. Levi, “What is the basis for this ruling? [10a] It is because [we hold the principle that] it is normal for weasels to uncover [a vessel] and not normal for them to cover it. Alternatively, the basis for the ruling is that he left it uncovered and came back and found it covered. Or he left it covered and came back and found it uncovered. But if he found it the same as he left it, [the water] is neither unclean nor unfit.” But consider if it is a case of doubt regarding [danger of poisoning in an instance of] uncovered water, it is prohibited. We derive from this the conclusion that we are stricter for [cases of doubt regarding] danger than we are for [cases of doubt regarding] prohibitions [of law]. We derive it.
C. It was taught there on Tannaite authority in the Mishnah, Three [kinds of] liquids are forbidden [for consumption] on account of [danger of poisoning in an instance of being discovered in a vessel that is] uncovered: (1) water, (2) wine, and (3) milk. [But all other liquids are permitted for consumption, even if left uncovered.] How much time must elapse [with them uncovered] before they become forbidden? Long enough for a snake to leave a nearby [hiding] place and drink [from them] [M. Ter. 8:4].
D. And how far away is a nearby place? Said R. Yitzhak the son of R. Judah, “Enough time for it to come out from under the handle of a vessel and drink [from the liquid]. [But if we say just enough time] to drink, lo, we will see it [drinking]. Rather [say that the time needed is] enough to drink and to return to its hole.”
A. It was stated: One who slaughters with a knife and it is [later] ascertained that it is defective — said R. Huna, “Even if he chopped bones with it all day [after slaughtering the animal with the knife] it is unfit. We suspect that perhaps it became defective on account of the hide [of the animal before he slaughtered the organs].” And R. Hisda said, “It is fit [because we can posit that] perhaps it became defective [while chopping] on a bone.”
B. R. Huna is consistent with his other teaching [i.e., “An animal in its lifetime remains in the presumptive status of forbidden [food] until it is known to you how it was slaughtered. Once it was slaughtered it remains in the presumptive status of permitted [food] until it is known to you how it became terefah” (above I.18 B)]. But what is the basis for the opinion of R. Hisda? He would say to you [to reason as follows]: [Cutting] a bone certainly renders [a knife] defective. [Cutting] hide may or may not render [a knife] defective. It is a [classic clash of a case of] doubt against [a case of] certainty. And [the case of] doubt does not [have the power to take priority over the case of] certainty.
C. Raba raised an objection [to Hisda] in support of the view of R. Huna. [We have a rule:] If one immersed [in a miqvah] and came out and found upon himself something [adhering to his body] that separates [it from the water], even if he was occupied with handling that substance all day long [after his immersion], his immersion is not effective for him until he declares, “I am certain that it was not [stuck] on me before [I immersed].” But lo, here [we have a case where] he was certain he immersed and he had a doubt whether it was stuck to him [before he immersed]. And the [case of] doubt comes along and takes priority over the case of certainty.
D. That case is different. For one could say that you should uphold the presumptive status of the unclean person and say that he did not immerse. Here too [say], you should uphold the presumptive status of the animal and say that it was not slaughtered. But lo, here is the slaughtered animal in front of you. Here too, lo the person who immersed is in front of you. But lo, [for the unclean person] there appeared a taint [of uncleanness]. Here too, [on the knife] there appeared a taint [of a defect]. [There is a conceptual difference between the cases.] [In the latter] a taint appeared regarding the knife. No taint appeared regarding the animal [itself]. [The taint is more removed and hence less significant because it relates to the knife and not the body of the animal itself.]
E. They raised an objection: If he slaughtered [a bird, which needs only one organ cut to render it fit], through the gullet and afterward the windpipe was displaced, it is fit. If the windpipe was displaced and afterward he slaughtered through the gullet, it is unfit. If he slaughtered through the gullet and afterward he found the windpipe was displaced and he did not know whether it was displaced before or after he slaughtered — this was an actual case and they said [they have the principle], “All cases of doubt in slaughtering are judged unfit.”
F. What [case] does the expression, “All cases of doubt in slaughtering” encompass? Does it not encompass this very matter [of a doubt regarding a knife as at A]? No. It encompasses a case where there is a doubt whether [in the act of slaughtering] he paused or pressed.
G. [10b] And what is the distinction [between these cases of doubt]? There [in the latter instances where he may have paused or pressed] a taint appeared in the animal. Here [in the case of a knife that may have become defective] a taint appeared in the knife. No taint appeared in the animal.
H. And the law accords with the view of R. Huna [in A in a case where] he did not chop bones [with the knife]. And the law accords with the view of R. Hisda [in A in a case where] he did chop bones [with the knife].
I. This implies that according to the view of R. Hisda [that the knife is fit] even if he actually did not chop bones with it. If so, how did it become defective? We could say it became defective from [cutting through] the neck bone [after severing the organs].
J. This was an actual case [i.e., a knife was found defective after a person had used it to slaughter several animals]. And R. Joseph declared terefah as many as thirteen animals. And on whose authority [did he declare them terefah]? According to the view of R. Huna. And [if so did he include as unfit] even the first one [that he slaughtered because Huna says the knife may have become defective as a result of cutting the hide of the first]. No. [He based his decision] on the view of R. Hisda [and he declared all of them unfit] except for the first one.
K. And another possibility: it is [more] consistent to conclude that he based his decision on the view of R. Huna. Because if he based it on the view of R. Hisda [one could argue] since [he based his view on the argument that] we may defer our judgment [and assume that the knife became defective from contact with a bone after slaughtering the animal] why say that [it became defective] from contact with the neck bone of the first animal? Perhaps [we should assume that] it became defective from contact with the neck bone of the last animal [he slaughtered].
L. Said to him R. Aha the son of Raba to R. Ashi, “R. Kahana required an inspection [of the knife] between [the slaughtering of] each and every [animal].” In accord with whose view [did he say this]? If in accord with the view of R. Huna, then he should declare the first one unfit [if the knife is not examined each time and is found defective]. No, in accord with the view of R. Hisda, and then he should say even the last animal may be deemed fit [if the knife is not examined and is found defective].
M. If this is the case [that we follow R. Hisda], we should require inspection by a sage. [Inspection by the slaughterer should not suffice.] [We do not require that rigorous inspection because the testimony of] one witness [i.e., the slaughterer] is trusted in matters pertaining to prohibitions. If so, then to begin with we also should not [ever require inspection of the knife by a sage]. Lo said R. Yohanan, “They only said that you must show the knife to a sage because of the respect due a sage.”
A. What is the source for this matter that the rabbis stated: uphold a matter on the basis of its presumptive status? Said R. Samuel bar Nahmani, said R. Jonathan, said Scripture, “Then the priest shall go out of the house to the door of the house, and shut up the house seven days” (Lev. 14:38). Perhaps while he was going out of the house the spot became smaller than the required size. Is it not logical to deduce that [he may presume this does not occur] because we say we uphold [the status of the house] on the basis of its presumptive status?
B. R. Aha bar Jacob raised this objection: Perhaps [in the case of the house the priest] went out of the house facing backward and he could see the spot while he was going out.
C. Said to him Abayye, “There are two responses [to your objection] in this matter. First, going out backward is not a valid way of going out. And further, [if the spot is located] behind the door [where the priest cannot see it as he exits] what can we then say?” And if you say that he opens opposite [the spot a window, so he may watch it as he walks out], lo it was taught in the Mishnah on Tannaite authority, In a dark house they do not open a window so as to examine its spot [M. Neg. 2:3].
D. Said to him Raba, “What you say — going out backward not being a valid way of going out — the case of the High Priest on the Day of Atonement should prove that you are wrong. For it was written, `Then he shall go out' (Lev. 16:18). And it was taught in the Mishnah on Tannaite authority, If he went out and left the way he went in... (b. Yoma 52b). [This implies he went out backward.] And what you say, In a dark house they do not open a window so as to examine its spot — this only applies to a case where the status [of the house as unclean] was not yet established. But once it is established, it is established [and he may open a window when he examines the spot].”
E. It was taught on Tannaite authority not in accord with R. Aha bar Jacob: “Then the priest shall go out of the house” — you might argue that he may go into his own house [to examine a spot in another house from there] and quarantine it. It comes to teach us [the phrase], “To the door of the house” [implying that he must go to the affected house]. If you just say, “To the door of the house,” you might argue that he may go [to the doorway] and stand under the lintel and quarantine the house. It comes to teach us [the phrase], “Out of the house” — [he does not fulfill the Scriptural injunction] until he goes out of the house.
F. What are the circumstances [of a proper examination]? He must stand next to the lintel [outside the house] and quarantine it [after the examination]. And on what basis do we say that if he went back to his own house [after examining another house] and quarantined it from there, or if he stood inside that house and quarantined it from there, that his quarantine is valid? It comes to teach, “And shut up the house” — anyway he does it [it is valid].