A braita rules that if one cuts an olive-bulk of flesh from a limb attached to a living animal, designating it for food only after cutting renders it pure, whereas designating it prior to cutting renders it susceptible to food impurity, as it touches the limb (which has high level impurity) as it is being cut. The Gemara presents Rav Asi's challenge to Rabbi Zeira as to why prior designation causes impurity, given that the cut site is a concealed place (tumat beit ha-satarim) and concealed impurity does not transmit impurity. Rava clarifies that the case involves a situation where liquids (hechsher) came upon it and Rabba bar Rav Chanan questions that, noting that it should not even require hechsher under the rule of an item destined to transmit severe impurity does not need hechsher, since here it came from a limb with a high level of impurity. Rava responds with a fundamental principle that when food functions as a connection or for a purpose other than food, it is considered "when used, it functioned like wood" and thus the rule of "destined to transmit severe impurity" does not apply. The Gemara presents five challenges that are resolved by applying this same explanation – "when used, it functioned like wood." Returning to the Mishna dealing with a dangling limb and flesh on an animal, the Gemara asks for the rationale of Rabbi Shimon, who rules them pure in the case of the animal's death, challenging his view as completely illogical. The Gemara suggests that Rabbi Shimon disagrees with the reisha (opening clause) of the Mishna when the animal is still alive, based on Rabbi Yochanan's explanation that Rabbi Shimon derives from scripture "מכל אשר יאכל" that food is defined as such only if you can feed it to others; since a dangling limb or flesh from a living animal is forbidden to consume even for non-Jews, it cannot transmit food impurity. However, Rabbi Zeira raises a difficulty, explaining that if Rabbi Shimon disagrees with that case, it is because the flesh and limb are still somewhat attached, as learned from a Mishna in Uktzin (3:8). Thus, Rabbi Yochanan's explanation of Rabbi Shimon's view must apply to another case. The Gemara suggests it might apply to the metzi'ata (middle clause) where the animal was slaughtered, but this resolution is also difficult. In light of these difficulties, the Gemara returns to understand Rabbi Shimon's statement and Rabbi Yochanan's explanation, concluding that they actually refer to the seifa (final clause), not regarding the dangling limb (from which the difficulty was raised), but rather regarding the dangling flesh. The Mishna discusses a dangling limb and flesh on a living human, ruling that they are pure during the person's lifetime. Upon the person's death, the flesh is pure from food impurity, while the dangling limb transmits impurity as a limb from a living person, but not as a limb from a corpse, according to Rabbi Meir. Rabbi Shimon considers it pure. The Gemara again challenges Rabbi Shimon's view in the same manner as before. As a first resolution, it explains that Rabbi Shimon disagrees with a general underlying premise of Rabbi Meir's view. Subsequently, however, the Gemara successfully understands Rabbi Shimon's position in a different manner, based on a Mishna in Eduyot 6:3.
