Pesachim 121A

חד תני אפיגול, וחד תני אנותר.

The Talmud explains that there is no dispute between Rav Huna and Rav Ḥisda concerning the reason for the prohibition. One of these two rabbis teaches his explanation with regard to the case of piggul, mentioned in the Mishnah; and the other one teaches it with regard to notar.

מאן דתני אפיגול ⁠— משום חשדי כהונה. מאן דתני אנותר ⁠— משום עצלי כהונה.

The Talmud elaborates: The one who teaches it with regard to piggul maintains that the reason is due to suspected priests. As a result of enmity, a priest might cause the offerings to become piggul. To dissuade priests from doing so, the rabbis instituted that one who touches piggul is rendered ritually impure, which ensures that the offending priest also suffers from his actions. He who teaches this explanation with regard to notar claims that the reason is due to lazy priests, to prevent sloth among the priests. The rabbis decreed that notar causes ritual impurity, to ensure that the priests ate the sacrificial meat within the allotted time.

חד אמר כזית וחד אמר כביצה. מאן דאמר כזית ⁠— כאיסורו, ומאן דאמר כביצה ⁠— כטומאתו.

It was stated above that Rav Huna and Rav Ḥisda disagree with regard to the size of the meat that confers ritual impurity. One of them said that an olive-bulk of meat contracts ritual impurity, and one of them said that only an egg-bulk contracts ritual impurity. The Talmud explains the reasoning behind this debate. The one who said that an olive-bulk contracts ritual impurity maintains that the ritual impurity of notar and piggul is similar to its prohibition. Since notar and piggul are prohibited when they are an olive-bulk, the same applies to their ritual impurity. And the one who said that sacrificial meat becomes ritually impure when it is an egg-bulk maintains that it is similar to its ritual impurity. In other words, just as the minimum size of ritual impurity for other types of meat is an egg-bulk, the same applies to piggul and notar.