A cat or a weasel (chulda) renders a bird a treifa through clawing (derisa), whereas only a cat can do so for small cattle such as young goats and lambs. Other predatory birds besides those explicitly listed in the Mishna can also render other birds a treifa by clawing, but only when targeting birds smaller than themselves, while a hawk (netz) can do so even to birds of its own size. According to an alternate version, ordinary predatory birds can claw birds of their own size or smaller, whereas the hawk can even render birds larger than itself a treifa. Furthermore, two conflicting versions are presented regarding Rav Kahana's ruling in the name of Rav Shimi bar Ashi concerning foxes, debating whether or not they possess the capacity to render animals a treifa through clawing. Abaye limits the laws of derisa to the predator's front legs, specifying that it must be executed specifically with a claw and not with teeth, must be done with intent, and must occur while the prey is still alive. In a case where a lion was found among oxen and a dislodged claw was subsequently discovered on the back of one of the oxen, Rabba bar Rav Huna ruled in the name of Rav that there is no concern for derisa. He reasoned that while most lions do claw, their claws do not generally detach in the process; thus, it is more probable that the ox rubbed against a wall and accidentally picked up a nail embedded there. The Gemara initially rejects this argument, countering that while oxen frequently rub against walls, nails rarely stick to their backs in this manner, and since the lion remains a viable source, one should rule stringently. Ultimately, the Gemara concludes that because the logic can support either side, the ox retains its presumptive status of permissibility; as a matter of pure doubt, Rav remains consistent with his opinion stated elsewhere that we rule leniently in cases of uncertain clawing. Abaye restricts this leniency, clarifying that it only applies when an actual claw is found embedded rather than a mere mark, when the claw is moist rather than dry, and when there are only one, two, or three claws scattered at random rather than two or three found in a distinct row. Rav and Shmuel disagree on whether to rule leniently or stringently in cases of doubt regarding derisa. While both agree to rule leniently in certain scenarios, they dispute a case where a lion entered among oxen and the lion remained silent while the oxen were found bellowing in distress. Ameimar ruled stringently in accordance with Shmuel, either because he rejected Rav's view or because he believed Rav ultimately retracted his opinion, a shift suggested by a practical incident that occurred. Although several difficulties are raised regarding the specific details of that incident, they are successfully resolved. Rav Ashi similarly ruled leniently in a case of doubt. If there is a doubt as to whether an animal was clawed, the Gemara rules that one may inspect the internal areas of the carcass to see if redness has formed from the venom; if no redness is present, the animal is permitted. This testing method was originally stated by the sons of Rabbi Chiya, though Rav Yosef pointed out that Shmuel himself had already articulated this principle. This discussion leads the Gemara to a series of inquiries - some regarding the laws of clawing and others concerning unrelated laws of treifot - all of which were concisely resolved by an authority who declared that each question had already been answered by a prior Rabbinic statement.
