• חיה בכלל בהמה ובהמה בכלל חיה

On the previous Daf, Rebbe Yonasan told בן עזאי that although there are clear pesukim that the נבילה of a בהמה טהורה (a kosher בהמה), a בהמה טמאה, and a חיה טמאה are metamei, there is none about a חיה טהורה. He quoted Rebbe Yishmael answering that since the Torah taught that the נבילה of a בהמה טמאה and a בהמה טהורה are tamei, the same applies to both types of חיות, because חיה בכלל בהמה – wild species are included in domestic species, ובהמה בכלל חיה – and domestic species are included in wild species. The former is derived from a passuk beginning with "בהמה", which proceeds to mention species of חיות. The latter is derived from a passuk beginning with "חיה", which then describes the סימנים for a kosher בהמה. He proceeds to teach that a חיה טהורה is included in בהמה טהורה regarding סימנים of kashrus. חיה טמאה is included in בהמה טמאה for the prohibition of הרבעה – crossbreeding. בהמה טמאה is included in חיה טמאה, which allows Rebbe to darshen a superfluous "בהמה" for a gezeirah shavah. בהמה טהורה is included in חיה טהורה for יצירה – “forming,” teaching (according to Rebbe Meir) that a woman who aborts something resembling a בהמה is tamei, just like if she had aborted something resembling a חיה.

• טומאה בלועה is not metamei, and טהרה בלועה does not contract tumah

Rabbah said: כשם שטומאה בלועה אינה מטמאה – just as a swallowed-up tamei item does not convey tumah to other objects, כך טהרה בלועה אינה מיטמאה – so too a swallowed-up tahor item does not contract tumah from something tamei. The first law is derived from the passuk: והאוכל מנבלתה יכבס בגדיו – and one who eats its carcass shall immerse (himself and) his clothing, and becomes tahor at nightfall. This means that even one who ate neveilah סמוך לשקיעת החמה – just before sunset becomes tahor at nightfall, even though the נבילה is still undigested in his stomach (and נבילה is normally metamei במשא – by being carried)! This proves that swallowed-up tumah is not metamei. We derive from a kal vachomer that טהרה בלועה does not contract tumah: a כלי חרס המוקף צמיד פתיל – earthenware utensil which is closed all around with a tight cover does not prevent tumah inside it from being metamei, because a dead body which is buried in the ground (without a tefach of airspace) is metamei anything above it, and the same certainly applies to a sealed כלי. Yet, a sealed כלי protects tahor items inside it from contracting tumah. If so, then a person, which does prevent tumah inside him from being metamei, certainly would protect tahor items inside him (e.g., a swallowed ring) from becoming tamei.

• טומאה בלועה is not even metamei טהרה בלועה (swallowing a tamei ring is not metamei a tahor ring)

Rava objects that both of Rabbah’s laws were clearly taught by a Mishnah: if a Kohen swallows a tamei ring, he may still immerse himself to become tahor from the initial contact with the ring and eat terumah, and the swallowed ring is not metamei him. That Mishnah also teaches that one who swallows a tahor ring, entered an אהל with a dead body, then completed the taharah process, and expelled the ring, it is tahor, because it did not contract tumah inside his body. What novelty is Rabbah teaching?

The Gemara answers that Rabbah’s ruling is כגון שבלע שתי טבעות – a case where one swallowed two rings, one which is tamei and one which is tahor. Thus, he teaches דלא מטמיא לה טמאה לטהורה – that the tamei [ring] is not metamei the tahor [ring], although they are both swallowed together.