Zevachim Daf 105 זבחים דַף 105

The Tanna Kamma of the previous Mishnah taught that as soon as פרים הנשרפים are carried out of the עזרה, they are metamei the people carrying them. Rebbe Elazar asked, if half the body was outside and half inside, and the majority of one limb was outside, do we say: האי מיעוטא דאבר בתר רוב אבר שדינן ליה – regarding this minority part of the limb left inside, we “throw” it after its majority to consider the entire אבר, and thereby the majority of the animal, outside? Or does it follow the majority of the animal (i.e., its actual location), and its majority has not yet left the עזרה? Rabbah bar Rav Huna taught this question בגברי – about men: where five people were involved in carrying the body, and three of them had left the עזרה while two were still inside. בתר רוב מתעסקין אזלינן – Do we follow the majority of those involved with the body, and those inside would also be tamei,  או בתר בהמה אזלינן – or do we only follow the majority of the animal, not of those carrying it? The Gemara concludes: תיקו.

The Torah says that "זרע" – [edible] seed is only susceptible to tumah after הכשר – preparation for tumah (i.e., becoming wet, and later contracting tumah). This model teaches that just as seeds, which will not be metamei with "טומאה חמורה" – severe tumah (i.e., as an אב הטומאה, which food can never become), require הכשר, the same applies to anything which is not metamei with טומאה חמורה. This excludes the neveilah of a kosher bird, שסופה ליטמא טומאה חמורה – which is destined to be metamei with a severe tumah, ואין צריכה הכשר – so it does not require הכשר, but is metamei food automatically. Rebbe Meir says that the bodies of פרים הנשרפים, the פרה אדומה, and the שעיר המשתלח, all of which are metamei those involved with their procedure with a טומאה חמורה (but are not metamei people through contact), are themselves metamei foods through contact. The Chochomim hold that although these items can be metamei on their own without contracting tumah from anything, they need to be susceptible to tumah. Thus, they agree that the פרים and פרה אדומה are מטמא foods, but hold that the שעיר המשתלח, which is alive and unfit for tumah, is not metamei foods.

According to Rebbe Meir, who said even items unfit for tumah can be metamei foods if they are destined to be metamei with "טומאה חמורה", there are cases where a כזית of a kosher bird’s נבילה would be metamei food (despite lacking the minimum size for tumah). Rav Hamnuna asked Rebbe Zeira: מונין בו ראשון ושני – do we count rishon and sheni levels of tumah from it, or not? Meaning, does the food it touched become a ראשון לטומאה, which can be מטמא other food as a שני? Or does the food it touched only become a שני? He answered that only something with the ability to be מטמא a person במגע – through contact, can be מטמא food as a ראשון and then a שני, but כל היכא דאין מטמא אדם במגע אין מונין בו ראשון ושני – anything which cannot be metamei a person through contact, we do not count rishon and sheni levels of tumah from it, rather, the food becomes a sheni. A similar question was asked regarding two half-כזיתים of נבילה which are attached with liquid, which are only considered connected for "טומאה קלה" – lenient tumah (i.e., foods), but not to be metamei people. Here, too, the foods they touch are only made a שני, since they cannot be metamei people.