Explanation #1: The Rivam explains that Rav Kahana asked Rav all the current She'eilos on different occasions; first he was studying birds, so he asked him whether D'rusah pertains to a cat, to which Rav replied 'It even pertains to a weasel!'; Then he was studying large sheep, so he asked him whether D'rusah pertains to a weasel, to which he replied 'It does not even pertain to a cat!', Finally, he was studying kid-goats and lambs, so he asked him whether D'rusah pertains to both a weasel and a cat, and he replied 'To a cat yes, but to a weasel, no!' ...

Precedent: ... and that is how he explained the Gemara in Perek Tolin (Shabbos 138a & b, DH Ba'a) where Rav Kahana asked Rav (regarding spreading a temporary Ohel) 'Kilah (a canopy) Mahu', to which the latter replied 'Even a bed is forbidden!', Then he asked him about a bed, to which he replied 'Even a Kilah is permitted'; and when he finally asked him about a Kilah and a bed, he replied 'Kilah Asurah, Mitah Muteres!', and there is no Kashya ... .

Explanation #2: Alternatively, Rav Kahana asked Rav all the above She'eilos in one sitting. First he asked him whether s cat is subject to D'rusah or not, to which he replied 'You ask S'tam'; there is a case where even a weasel is!' Then he asked him whether a weasel is always subject to D'rusah, to which he replied that sometimes even a cat is not. Finally, he asked him whether, since there are occasions where both a cat and a weasel are subject to D'rusah, and sometimes are not, the two are equal, and he answered that there are cases where a cat is subject to D'rusah, but a weasel is not ...

Precedent: ... nd it is possible to explain the Gemara in Shabbos in the same way.

Clarification (Part 1): This D'rusah refers to where the bird injects its venom as it withdraws its claws ...

Clarification (Part 2): ... and it is therefore unconnected to the Gemara later (on Daf 59a) where it states that every bird that is Doreis is Tamei, which is one of the Simnei Tum'ah of a bird ...

Clarification (Part 3): ... and the Gemara's She'eilah is restricted to Tamei birds, but it is obvious that Tahor birdsare not Doreis.

Question: Why does the Gemara not answer that here it is speaking about a small lamb, whereas Rav Kahana is referring to laege sheep?

Answer: Because if he was, why does he mention a fox, when he could just as well have mentioned a cat?

Question: Why does he not answer that this case involved a large sheep, And so it would seem, seeing as it mentions a sheep and not a lamb.

Answer: Because then Rav Dimi would not be teaching us any Chidush with this story, since even a cat is not subject to D'rusah with regards to a large sheep.

Refutation: There are some who err, inasmuch as they permit Shechting a bird on which a hawk is lying, as long as it has not removed its claws from it, since it has therefore not yet injected it with its venom.

Reason: This is forbidden however, since when a hawk chases and captures its prey, it strikes it with its claws repeatedly, in which case it is Doreis and withdraws a number of times.

Question #1: Even if we assume that this claw is the result of scratching, bearing in mind that most lions are Doreis when they enter a herd of oxen, we ought to suspect (D'risah) even with regard to the other oxen which do not have a claw?

Question #2: And by the same token, when Abaye says shortly ' ... but the location of the claw we suspect (D'risah)'. Why does he need to mention 'the location of the claw at all'?

Answer/Explanation (Part 1): Rabeinu Tam explains as follows: 'The majority of lions are Doreis (are fit to be Doreis, seeing as they are healthy and are able to do do); whereas a minority are sick and are therefore not able to be Doreis.

Answer/Explanation (Part 2): ... Now the claws of healthy lions that are Doreis do not usually become detached. Consequently, this lion, whose claw was settled on the ox's back, was probably sick, and the claw did not come on the ox's back due to D'risah, but rather when the ox scratched itself against the wall and the lion's foot that was lying next to it. That was when the claw detached itself and settled on the ox's back.

Answer/Explanation (Part 3): The Gemara then asks 'On the contrary, even though most oxen scratch themselves, most oxen tend not to do so in the vicinity of a lion's foot, in which case, we ought rather to attribute the claw in its back to the lion's D'risah ...

Answer/Explanation (Part 4): ... despite the fact that the claws of the majority of healthy lions that are Doreis do not generally becomes detached.

Answer/Explanation (Part 5): And the Gemara therefore concludes that since we can learn either way, Rav follows his opinion which does not contend with Safeik D'rusah, since we place the ox on its Chazakah of not being a D'rusah.

Clarification (Part 1): The word 'Kol' is La'av Davka', as it is in the Gemara that we will learn shortly 'Every ox that scratches ... '.

Clarification (Part 2): ... and what it really means is 'the majority of lions that are Doreis', and 'the majority of oxen that scratch'.

Explanation #1: 'A bird's-nest', since the Targum of the Pasuk in Tehilim (84) "u'Deror Kein lah" is 'Shirk'fa'.

Explanation #2: Rashi however, translates it as 'a basket full of birds'.

Implied Question: Then why does the Gemara say later in the Perek (58a), in connection with eggs of a Safek T'reifah that the first batch we put aside, and if it lays any more eggs, they are permitted? Why are we not worried there too, about Takalah?

Answer #1: However, the Gemara says in the first Perek of Pesachim (Daf 20b) that whether we are concerned about 'Takalah' or not is a Machlokes Tana'im.

Answer #2: Moreover, if the Safek T'reifah is going to lay more eggs, it will do so very quickly (in which case the fear of Takalah is not so applicable).

Answer #3: And thirdly, according to the conclusion here, that what Shmuel did, he did in order to publicize the fact that they were Asur (and not because of Takalah), there is no problem.

Reference: Tosfos already explained this earlier on Daf 28a DH Asa).

Question (Part 1): At the beginning of 'Ta'aroves (Zevachim 74b) the Gemara asks, with regard to where an animal became mixed up with a T'reifah 'How is this T'reifah speaking? If he recognizes it, let him remove it, and if not, how he does he know that it is a T'reifah?'

Question (Part 2): ... to which Rebbi Yanai answers that 'An animal that was pierced by a thorn became mixed up with a D'rusas ha'Ze'ev'; Resh Lakish ... 'with a Nefulah', and Rebbi Yirmiyah ... 'with the child of a T'reifah', and the author is Rebbi Elazar.

Question (Part 3): The Gemara then goes on to explain that the other two opinions decline to learn like Rebbi Yanai, because one can discern the difference between a Nekuvas ha'Kotz and a D'rusas ha'Ze'ev, in that the latter is elongated whereas the former is round.

Question (Part 4): In that case, by the same token, it should also be possible in our case to discern as to whether it was a cat (elongated) or a cane (round)?

Answer: The Gemara's distinction applies there from a wolf and upwards, but the claw-mark of a cat is not discernable.

Question: Then why did the Gemara there not answer that it is speaking about kid-goats and lambs, where a Nekuvas ha'Kotz became mixed up with the D'rusah of a cat.

Answer: The Gemara preferred to establish the case by all animals.

Implied Question: Why did it not then differentiate between a D'rusas ha'Kelev and a D'rusas ha'Ze'ev?

Answer: Perhaps it is possible to discern between them.

Explanation #1: Rashi establishes the Gemara with regard to a Safek that a lion performed D'risah on it, or where it definitely did, only the location of the D'risah is not discernable from the outside.

Inference: This implies that Bedikah does not help by Vaday D'risah; and that is also the opinion of the Rivam, z.l., who explains that Vaday D'risah is not subject to Bedikah, since sometimes the flesh turns red, making it difficult to assess accurately.

Explanation #2: It seems however, that Bedikah is effective, even by Vaday D'rusah ...

Proof #1: ... since the Gemara will say shortly that 'by a D'rusah, until the flesh beside the intestines turns red, whereas with regard to the Simanim, only if they themselves turn red, but if it is merely the flesh next to them that is red, the animal is Kasher, even though the fact that it turned red (the result of the venom) indicates that it is a Vaday D'rusah.

Proof #2: Furthermore, the Gemara will also say shortly that 'Rav required Bedikah from the pan of the scull till the thigh' - which can only refer to a Vaday D'rusah, seeing as he did not retract (from his position exempting Safek D'rusah from Bedikah) - as Rashi explained above, based on the Gemara in 'Kol Gagos' (Eruvin 94a).

Implied Question: Then why did the Gemara state at the beginning of the Perek (43a) 'Nafka Minah le'Safek D'rusah', and not 'leVaday D'rusah'?

Answer #1: Because le'Halachah, we are also concerned about Safek D'rusah.

Answer #2 (Part 1): Moreover, since the Gemara will shortly ask that 'Since a Mashehu hole in the Veshet is T'reifah, so too, is a Mashehu D'rusah. But what is the Shi'ur D'risah of a Kaneh, whose Shi'ur for a hole is the size of an Isar?' ...

Answer #2 (Part 2): ... from which we see that even though the smallest amount may well turn red, it may not be considered D'risah until it has affected the Shi'ur of an Isar.

Conclusion (Part 1): It therefore appears that also Rashi only mentions Safek D'rusah, because then one is required to examine everywhere - the animal's back, its stomach and sides, and the entire area that borders the intestines.

Conclusion (Part 2): ... whereas if it was discernable from the outside, it would only require examination at that spot.