As we learned on yesterday’s daf (=page), not all holes discovered in an animal’s lung automatically render it non-kosher. Even in cases where the assumptions that we learned about do not apply, there are tests that can be performed to clarify where the hole came from and whether the animal must be declared a terefah because of it. Thus, we learn on today’s daf, that Rabbi Yohanan and Rabbi Elazar agree that if a hole is found on an animal’s lung – and it cannot be attributed to a factor that would allow the animal to be permitted – a similar hole can be made so that a comparison can be performed. If the two holes look the same, we can assume that the first hole – like the second one – developed after the animal was slaughtered and the animal is considered kosher.
Rava suggests that the comparison can only be made on a single lung, but cannot be made from one lung to the other. This suggestion is rejected by the Gemara. The Gemara concludes, however, that comparisons can only be made between similar animals – one gasah (a large animal) to another or one dakah (a small animal) to another– but cannot be made between a gasah and a dakah.
This last ruling follows Rashi‘s first interpretation of the Gemara, as well as that of the Rambam and Rabbenu Hananel. Rashi expresses doubt about this ruling, arguing that any comparison between two different animals cannot be reliable, even if the animals are similar. For this reason he prefers an alternative explanation of gasah and dakah in this case, where they refer to the larger lobes or the smaller lobes of the lungs, so that only similar lobes can be compared.
The clear ruling of the Gemara notwithstanding, the Rema (Shulhan Arukh Yoreh De’ah 36:5) argues that we are no longer expert in this method and that there is no longer a tradition to rely on tests like these to permit an animal.