We begin our study with the Mishnah, which states that the blood of a Sheretz and its flesh combine to form the requisite measure for ritual impurity. We know that the flesh of a Sheretz combines to form this measure, and the novel aspect here is that its blood also combines. This combination is necessary to reach the minimum measure for ritual impurity.
The Gemara elaborates on this principle of combination. For items to combine, two conditions must be met: the level of impurity must be the same, and the minimum measure for impurity (the shiur) must also be the same. For example, in the case of the eight creeping things (Shemona Sheratzim), a weasel (choled) and a mouse (akhbar) are two such creeping things. They both impart impurity of the same level and require the same measure. Similarly, two pieces of a carcass (nevelah) both impart impurity of the same level and require the same measure, and thus they combine.
However, if the level of impurity is the same but the shiur is not, they do not combine. For instance, both a limb from a corpse (ever min ha'met) and flesh from a corpse (basar min ha'met) impart impurity for seven days and can impart impurity through touch, carrying, or in a tent (maga, masa, ohel). Yet, the shiur for flesh from a corpse is an olive's-worth (kezayit), while for a limb from a corpse, it is any amount (kol shehu). Since their shiurim differ, they do not combine.
Conversely, if the shiur is the same but the level of impurity is not, they also do not combine. For example, a carcass (nevelah) and flesh from a corpse (basar ha'met) both require a shiur of a kezayit. However, a nevelah imparts impurity for one day, while a corpse imparts impurity for seven days. Since their levels of impurity differ, they do not combine.
Naturally, if neither the level of impurity nor the shiur is the same, they certainly do not combine. For example, a creeping thing (sheretz) and a carcass (nevelah) have different shiurim (a sheretz is any amount, a nevelah is a kezayit). Furthermore, a sheretz imparts impurity through touch, while a nevelah imparts impurity through touch and carrying. Thus, they do not combine. In summary, for items to combine, both the level of impurity and the shiur must be identical.
Rav Hanin said in the name of Rav Zeira, regarding the statement that the blood of a Sheretz combines with its flesh: this refers specifically to the blood and flesh of the same Sheretz. It does not mean that the blood of one Sheretz combines with the flesh of another Sheretz. The blood of a Sheretz combines only with its own flesh.
However, Rabbi Yosef bar Rabbi Hanina challenged this. He cited a verse regarding the Shemona Sheratzim which states "HaTemim" (the perfect ones). The extra "Heh" in "HaTemim" teaches that these different creeping things can combine with each other. This implies that even different species of creeping things can combine. Not only can the flesh of one Sheretz combine with the blood of the same Sheretz, but even the blood of one species (e.g., a mouse) can combine with the flesh of another species (e.g., a weasel). This contradicts the assertion that combination is limited to the blood and flesh of the same Sheretz.
In response, Rav Yosef clarified that the Baraita allowing combination between different species refers to a case where one touches the entire creeping thing, meaning both its blood and flesh, even if they are from different species. However, if one touches only a part of it—either just the blood or just the flesh—and the blood and flesh are not from the same Sheretz, they do not combine. Each part is considered separate, and therefore, the requisite shiur for impurity is not met. Combination occurs only when the blood and flesh come from the same Sheretz, in which case they are considered one entity, and touching even a part of it (e.g., just the blood) is sufficient to impart impurity as if one touched the whole.
To support this distinction between touching the whole versus touching a part, Rav Yosef brought a proof from the law of a "yavrivi'it" (a small amount) of blood from a corpse that falls on the floor. A yavrivi'it of blood from a corpse imparts impurity through touch, carrying, and in a tent. If this blood falls on the floor and spreads out on an incline (katafres), it is not considered collected in one area. If someone touches only a part of this spread-out blood, they remain pure, because the blood is not considered connected. However, if they touch the entire spread-out blood, they become impure. This demonstrates that for items not considered connected, one must touch the entire amount to contract impurity. Similarly, if the blood and flesh of a Sheretz come from different items, they are not considered connected, and therefore one must touch the entire combined amount to become impure.
Rabbi Zeira offered another proof, citing the case of a stirrer (magis) used in blood from a corpse. If one stirs blood from a corpse, the stirrer itself remains pure, even though it is touching the blood. This is because some blood is absorbed into the spoon, and thus the blood on the spoon is not considered connected to the blood in the bowl. As a result, the combined amount on the spoon and in the bowl does not reach the requisite shiur for impurity. This further illustrates that when items are separate, even if touching, they do not combine to form a single entity for impurity purposes, unless the entire quantity is touched. The same principle applies to the blood and flesh of a Sheretz: if they are from different sources, they are considered separate, and one must touch the entire amount for impurity to be contracted.
The Gemara then shifts to a different topic. Rabbi Matia ben Harash asked Rabbi Shimon ben Yochai in Rome, "From where do we know that the blood of creeping things (dam sheratzim) is ritually impure?" It wasn't obvious that the blood of a Sheretz, which is inherently impure, would also be impure. Rabbi Shimon responded by deriving it from an extra letter "Vav" in the verse "Ve Ze Lachem HaTameh" (And this shall be impure for you). This extra "Vav" comes to include the blood of a Sheretz. Rabbi Shimon's students were greatly impressed by this astute derivation.
However, Rabbi Matia ben Harash replied, "What are you so excited about, Rabbi Shimon? This is not your own wisdom! This teaching was already taught by Rabbi Elazar bar Rabbi Yose." The Gemara then recounts the famous story of how this teaching came to be known.
The Roman government had issued three decrees against the Jewish people: they were forbidden to observe Shabbat, to circumcise their sons, and to immerse women after menstruation (niddot) in a ritual bath (mikveh). Rabbi Reuven ben Istratbulis disguised himself by growing his hair in a particular style and infiltrated the Roman Senate. He then cleverly argued against each decree. Regarding Shabbat, he asked, "Do you want your enemies to be rich or poor?" They replied, "Poor." He said, "Then let them observe Shabbat, for taking a day off will make them lose business." They agreed and rescinded the Shabbat decree. Regarding circumcision, he asked, "Do you want your enemies to be weak or strong?" They replied, "Weak." He said, "Then let them circumcise their children, for it causes bleeding and weakens them." They agreed and rescinded the circumcision decree. Regarding niddot, he asked, "Do you want your enemies to multiply or diminish?" They replied, "Diminish." He said, "Then let them not immerse after menstruation, for this will prevent them from conceiving for two weeks each month, thus minimizing their population." They agreed and rescinded the niddah decree. The Romans were about to implement these decrees, but Rabbi Reuven successfully had them overturned.
After this, the Romans realized they had been tricked. They needed someone else to go to Rome to reverse the decrees. Rabbi Yosef volunteered, but his father, Rabbi Yehoshua ben Levi, expressed concern, saying, "If my father were alive, would he allow me to go on such a dangerous mission?" Rabbi Yehoshua ben Levi then said, "I am more concerned about the anger of the heavenly court (bishva) than about the Romans. If the bishva becomes angry, it can turn a person into a pile of bones." He ultimately decided to go himself, fearing for his son's safety more than his own.
When Rabbi Yehoshua ben Levi was asked in Rome how we know the blood of a Sheretz is impure, he answered in a low voice, not wanting to publicly contradict Rabbi Shimon ben Yochai, his teacher. However, his lips were seen moving, indicating he knew the answer. For this, he was punished: his son would not return to him.
A demon (shed) named Ben Temarion offered to help them overturn the decrees. Rabbi Yehoshua ben Levi chose to accept the demon's help, reasoning, "What is the glory of my father's house? My great-grandmother Hagar had angels appear to her three times, and I get a demon? Still, wherever the miracle comes from, we will take it."
The demon entered the body of the Caesar's daughter, causing her to go mad. Rabbi Yehoshua ben Levi was called to heal her. He commanded the demon to leave, and she was cured. The Romans, grateful, told him to ask for anything he desired. They brought him to the treasury, where he found the document containing all the decrees against the Jews. He took the paper and tore it up.
Rabbi Yosef later recounted, "I saw the curtain (parochet) in the Roman treasury, and it had bloodstains on it." This was relevant to a halachic debate about whether the blood of the sin-offering was sprinkled on the floor in front of the Ark cover (kaporet) or directly on the kaporet itself. Rabbi Yosef's observation of bloodstains on the parochet supported the opinion that the blood was indeed sprinkled on the kaporet, as the parochet was positioned nearby. The bloodstains were not concentrated in one area but were spread out like a whip, indicating a sprinkling motion.