GEMARA: Rabbi Abba said that Rav Ḥiyya bar Ashi said that Rav said: If a bird flew under the flaps of one’s clothing on Shabbat and cannot get out, he may sit and secure it until dark and then take it. Rav Naḥman bar Yitzḥak raised an objection based on that which we learned in the mishna: If the first person sat in the doorway and filled it, and a second person came and sat next to him, the first person is liable and the second is exempt, even if the first person stood and went. What, does this not mean here, as it does throughout tractate Shabbat, that he is exempt after the fact, but it is prohibited to do so ab initio? How then could Rav say one may sit and secure the bird ab initio? The Gemara rejects this: No, the statement in the mishna means that he is exempt and it is permitted ab initio. The Gemara adds: So too, it is reasonable to explain the mishna that way from the fact that it was taught in the latter clause of the mishna: To what is this second person’s action similar? To one who locks his house to secure it, and it turns out a deer that was trapped before Shabbat is also secured inside it. By inference, he is exempt and it is permitted, just like one who locks the door to his house. The Gemara concludes: Indeed, learn from it that it is so.

Some say a slightly different version. Rav Naḥman bar Yitzḥak said: We too learned support for Rav’s statement in the mishna: Even if the first person stood and went, the first person is liable and the second is exempt. What, does this not mean that he is exempt, and it is permitted? The Gemara rejects this: No, he is exempt and it is prohibited. Rav Naḥman said: That is impossible, from the fact that it is taught in the latter clause of the mishna: To what is this second person’s action similar? To one who locks his house to secure it and it turns out a deer that was trapped before Shabbat is also secured inside it. By inference, he is exempt and it is permitted, just like one who locks the door to his house. The Gemara concludes: Indeed, learn from it that it is so.

With regard to this issue Shmuel said: With regard to all exempt rulings in the halakhot of Shabbat, although one who performs the action is exempt by Torah law, his action is prohibited by rabbinic law, with the exception of these three for which he is exempt and it is permitted to perform the action.
One is this case of the deer. And from what source do we conclude that one is exempt and it is permitted? From the fact that it was taught in the latter clause of the mishna: To what is this second person’s action similar? To one who locks his house to secure it and it turns out a deer that was trapped before Shabbat is also secured inside.
And another example where he is exempt and it is permitted is: One who drains an abscess containing pus on Shabbat, if he did so to create a permanent opening in it, he is liable. However, if he did so to drain fluid from it, he is exempt. And from what source do we conclude that one is exempt and it is permitted? As we learned in a mishna: A hand needle used for sewing clothes may be moved on Shabbat to remove a thorn. Apparently, removing a thorn on Shabbat is permitted ab initio to the extent that one is even permitted to move a needle for that purpose.
And another case is: One who traps a snake on Shabbat, if he deals with it so that it will not bite him and in doing so traps it, he is exempt. However, if he traps it for medicinal purposes, he is liable. And from what source do we conclude that one is exempt and it is permitted? As we learned in a mishna: One may overturn a bowl on top of a lamp ab initio on Shabbat so that the fire will not take hold in the ceiling beam; and similarly, one may overturn a bowl on top of a child’s feces so that he will not touch it and dirty himself, and on top of a scorpion so it will not bite, and the ruling is the same with regard to a snake.

MISHNA: With regard to any of the eight creeping animals mentioned in the Torah, one who traps them or wounds them on Shabbat is liable. The Torah states: “The following shall be impure for you among the creeping animals that swarm upon the earth: The weasel, and the mouse, and the dab lizard of every variety; and the gecko, and the land-crocodile, and the lizard, and the skink, and the chameleon” (Leviticus 11:29–30). With regard to other abominations and crawling things, one who wounds them is exempt. One who traps them for a specific need is liable; one who traps them for no specific need is exempt. With regard to animals or birds that are in his possession, i.e., an animal that is domesticated and under someone’s control, one who traps them is exempt; and, however, one who wounds them is liable.

GEMARA: The Gemara asks: From the fact that it is taught in the mishna: One who wounds them is liable, by inference they have skins. One is liable for inflicting a wound only when there is skin covering the flesh and the blood pools beneath it. Who is the tanna who teaches this? Shmuel said: It is Rabbi Yoḥanan ben Nuri, as we learned in a mishna that Rabbi Yoḥanan ben Nuri says: The eight creeping animals that are listed in the Torah have skins. Their flesh transmits impurity, but their skin does not transmit impurity. The Rabbis say that both the skin and the flesh of some creeping animals transmit impurity. Rabba bar Rav Huna said that Rav said: Even if you say that the mishna is in accordance with the opinion of the Rabbis, the Rabbis disagree with Rabbi Yoḥanan ben Nuri only with regard to the matter of impurity, as it is written after the Torah lists the creeping animals: “Those are for you the impure among the creeping animals, whoever touches them when they are dead shall become impure until evening” (Leviticus 11:31). The Rabbis derive from the extraneous term: “Those are for you the impure,” to include the fact that the skins of the creatures in the second verse transmit impurity just as their flesh does. However, with regard to the halakhot of Shabbat, even the Rabbis concede that their skin is distinct from their flesh.

The Gemara asks: And, with regard to Shabbat, they do not disagree? Wasn’t the following taught in a baraita? One who traps one of the eight creeping animals mentioned in the Torah or one who wounds them is liable; this is the statement of Rabbi Yoḥanan ben Nuri. And the Rabbis say: The term skin is utilized only