Implied question: Regarding Ben Dama, R. Yishmael's nephew (he was bitten by a snake, and a heretic came to cure him. He wanted to prove that it is permitted. He died before giving his proof), it says in Avodah Zarah (27b) that he did not transgress his colleagues' words, for it says "u'Foretz Geder Yishchenu Nachash";

There was no cure, for he died!

Answer: There, no cure was prepared for him. Here, the cure was prepared, and it was lost from him through bad Mazal, so it says that there is no cure.

Inference: Here it connotes that a snake loves Shachalayim (cress).

Support: At the end of Nedarim (91b), an adulterer told the husband "don't eat from this cress. A snake tasted it!"

Implied question: If so, Giluy applies to it (if it was left uncovered, one may not eat it, lest a snake tasted it and put venom in it). However, in Avodah Zarah (30b), it says that Giluy does not apply to cress!

Answer #1: There it does not refer to true cress, rather, to what it says there (Avodah Zarah 67a) "and so they used to do on Erev Shabbos in Tzipori. They put vinegar in beans, and called it Shachalayim."

Answer #2: In Nedarim, it discusses when there was vinegar in [the cress], like we concluded there in Avodah Zarah (30b) "but if there is vinegar in the cress, this is Migri (arouses snakes)." Also here, wine (with the cress) arouses them. (This is unlike Rashi and Tosfos explained there, that if it has vinegar, it deters snakes.)

Correction: R. Tam erased all this from his Sefer, and said that the text does not say so [here], rather, in Pesachim (42b).

Explanation (Ri): He erased it because one may drink Zeisum ha'Mitzri, like it says below (156a) that all agree that one may mix Shasis (Kali and vinegar) on Shabbos, and one may drink Zeisum ha'Mitzri. (Here we forbid Mei Dekarim!)

Rebuttal (Riva): There is no need to erase it. Rav Yosef does not come to explain Mei Dekarim of our Mishnah. Rather, he refers to Ula's teaching, that beer of Bavel is better [than Mei Dekarim]. Rav Yosef says that Zeisum ha'Mitzri is better than them.

Disclaimer: [The Gemara] connotes like Rashi explained, that [Rav Yosef] refers to [Mei Dekarim of] our Mishnah, since he did not explicitly say "Zeisum ha'Mitzri is better than them" (both of them; alternatively, Mei Dekarim, which is grammatically plural)!

Implied question: Why didn't [the Gemara] say that the Siman is Samech Samech, like it said above (66a)?

Answer: This is because Sa'arei (barley) is not spelled with a Samech. (However, Sisani is a good Siman, for begins with the sound of "S" twice, an allusion to Rav YoSef and Sa'arei.)

Question: Even if castration were not forbidden, we should ask that it is Asur [to cause sterility] due to Peru u'Rvu!

Suggestion: We could have answered that [it is permitted] for one who has children.

Rejection: In Yevamos (65b), regarding R. Chiya's wife, it connotes that if she were commanded about Peru u'Rvu, she would not have drunk a potion that sterilizes, even though she had two daughters and two sons, due to "ba'Boker Zera Es Zar'echa vela'Erev Al Tanach Yadecha" (even one who has children, should have more children)!

And in the conclusion (here, 111a) we establish according to R. Yochanan ben Brokah, who obligates [women in Peru u'Rvu], we establish [our Mishnah] to discuss a woman to whom castration does not apply, i.e. she is sterile or old. We do not establish it when she has children!

Answer: [The Makshan] preferred to ask from castration, because there is an opinion in Yevamos (61b) that once one fulfilled Peru u'Rvu, he need not [try to have more children].

Explanation: The Drashah is from [the suffix] "Chem" (there should not be castration in you).

Implied question: In Chagigah (14b), they asked Ben Zoma when one may castrate a dog, and he answered "uv'Artzechem Lo Sa'asu" - do not do (castrate) anything in your land!

Answer: There, he expounds "Eretz", like it explains in She'altos of Rav Achai, for [castration] is an obligation on the person. There is no difference between Eretz Yisrael and other lands! Rather, ba'Aretz comes to teach everything in the land. Here we expound "Chem", like I explained.

Explanation #1: The She'altos explained that the Isur to drink a sterility potion is like R. Yehudah, who forbids Davar she'Eino Miskaven;

Even though we hold like R. Shimon, who permits [Davar she'Eino Miskaven], this is only for Shabbos, because we require Meleches Machasheves, but in the entire Torah, we hold like R. Yehudah.

Rebuttal #1 (Ri): In the entire Torah, we hold like R. Shimon, who permits, like it connotes above (81b). We say that R. Yochanan holds like a Stam Mishnah, that a Nazir may smooth his hair and separate the hairs. This is like R. Shimon, who permits Davar she'Eino Miskaven.

Rebuttal #2: Also in Bechoros (34a), Shmuel holds like R. Shimon in the entire Torah, that Davar she'Eino Miskaven is permitted, regarding letting blood from a Bechor. Shmuel ruled like R. Shimon, who permits letting blood [even though it might blemish it];

The Gemara asks "until now, did Shmuel not teach that Davar she'Eino Miskaven is permitted? R. Chiya bar Ashi said..."

If there is a distinction between Shabbos and elsewhere, he needed to rule like R. Shimon, even though he already taught that regarding Shabbos, the Halachah follows R. Shimon!

Explanation #2: Here, [the Isur to drink a sterility potion] is even like R. Shimon, for it is a Pesik Reishei. He will surely become sterile through drinking the potion.