Rabba bar Rav Huna said in the name of Rav: If a lion had entered amidst oxen and later there was found a nail from a lion’s claw lodged in the back of one of them, there is no fear that the lion had clawed it. Why? Because although most lions attack with their claws there are a few that do not; moreover, all that do claw do not usually lose a nail, therefore the fact that this ox has a nail lodged in its back suggests that it had rubbed itself against a wall.
Rabbeinu Tam expresses surprise at the Gemara’s willingness to assume that most attacking animals do not lose nails from their claws, which leads to a conclusion that we need not be concerned with attacks in such cases. Surely since the majority of lions attack, once we ascertain that the lion was among the cattle all of the animals will need to be checked lest they were attacked! He concludes that when the Gemara states that “the majority of lions attack” it refers to healthy lions, and the minority that do not attack are sickly lions. Since healthy lions do not ordinarily lose the nails from their claws we can conclude that in this case the nail found on the ox did not come from an attack by a healthy lion. We therefore do not need to be concerned about the other oxen.
The Gemara continues, concluding that there are cases where we must fear that the animal was truly attacked:
Abaye said: This is the rule only when the nail was actually there, protruding from the back of the ox, but if there was found the mark of the nail of a claw upon the back, we are certainly apprehensive about it. And even when the nail was actually there this rule applies only if the nail was moist with blood, indicating that it was well attached to the lion, but if it was dry it is quite usual for it to fall loose while clawing. And even when the nail was moist the rule applies only to a single nail, but if there were two or three nails upon the back of the animal we are apprehensive about it (as multiple nails are not likely to be embedded in a wall); provided, however, they were in the shape of a paw.