A small (sparrow) hawk can render small fowl terefah by clawing them, and a large hawk (falcon) can do it to large fowl. Clawing makes an animal terefah only if done with the foreleg, not hind leg and not a tooth, and not if the paw was severed before the predator drew it back.
If a lion entered among the oxen, and subsequently a detached lion's claw was found embedded in the back of one of the oxen, we have two ways to reason. On the one hand, majority of lions do claw, and minority does not. That majority that claws usually does not leave a nail detached. Hence we might conclude that the ox rubbed himself against a wall and had the claw embed itself into its back. Or we can say that although most oxen rub themselves against the wall, but a claw does not usually become embedded in them, so perhaps this one was clawed. Rav, who rules leniently in cases of doubtful clawing, will declare the animal kosher, but Shmuel will say that it is terefah.
An animal that was possibly clawed needs to be examined for the typical signs, the reddening of the meat.
Art: Geza Vastagh - The British Lion