1. בשר מת inside a dead dog in the entrance of a house

A Mishnah states: הכלב שאכל בשר מת – if a dog ate flesh from a dead body, and the dog died and is lying with its neck in the threshold of a house, and its body (containing the בשר מת) outside, there are four opinions. Rebbe Meir says: יש בצוארו פותח טפח – if there is a tefach of space in its neck (i.e., its neck measures a cubic tefach), the tumah enters the house through אהל; otherwise, it does not. Rebbe Yose’s statement is interpreted in two parts: (1) רואין – we assess if there is a cubic tefach of airspace inside the dog’s neck to convey tumah (unlike Rebbe Meir, who includes the neck itself in the tefach). (2) Although Rebbe Meir holds that tumah transfers wherever the dog’s mouth is in the threshold, Rebbe Yose says this applies only מכנגד השקוף ולפנים – if its mouth is from the doorstop and inwards. Rebbe Elazar says that if its mouth is inside the house, the house is tamei, but if its mouth is outside (and its hindquarters are inside), the house is tahor, טמא מפני שטומאה יוצאה דרך שוליו – because the tumah exits through its hindquarters. Rebbe Yehudah ben Beseira says that either way, the house is tamei.

1. שלש טומאות פורשות מן המת

Rebbe Shimon says: שלש טומאות פורשות מן המת – there are three טומאות which emerge from a dead body, שתים בכל אחת ושלישית אין בהן – each of which has two of a מת’s abilities to transmit tumah, but lacks the third. [Rashi notes that there are many other טומאות of a מת, such as a כזית of flesh, but those transmit tumah in all three methods of מגע, משא, and אהל.] (1) מלא תרווד רקב – a ladleful of decomposed corpse-dust is metamei through משא and אהל, but not through מגע (since one cannot be in contact with the entire ladleful at once). והיכן מגעו – Where, then, is [tumah from a מת through] contact? עם אחת מהן – With either of [the other two] below. (2) עצם כשעורה – a bone the size of a barleycorn is metamei through משא and מגע, but not through אהל (this is known through a הלכה למשה מסיני). (3) גולל ודופק – The wall and cover of a coffin are metamei through מגע and אהל, but not משא. [Rashi discusses the source for this distinction.]

1. עכבר שחציו בשר וחציו אדמה

The next Mishnah states: עכבר שחציו בשר וחציו אדמה – Regarding a dead mouse which is half flesh and half earth, the Tanna Kamma says one who touches the flesh is tamei, but one who touches the earth remains tahor. Rebbe Yehudah says אף הנוגע באדמה שכנגד הבשר טמא – even one who touches the earth opposite the flesh is tamei. Rebbe Yehoshua ben Levi says: והוא שהשריץ על פני כולו – this ruling only applies if it developed into a שרץ over [one] entire side; otherwise, even touching the flesh would not render him tamei. Others teach this statement specifically regarding Rebbe Yehudah’s ruling that even touching the earth opposite the flesh is tamei. Accordingly, Rebbe Yehoshua ben Levi says that touching earth is only metamei if the entire other side of the mouse has developed as a שרץ. According to this version, touching the flesh of the mouse can be metamei even if it has not fully developed into a שרץ across one entire side.