The Pnei Yehoshua addresses both of your questions.

1. We discussed your first question in the Insights, which I include below.

2. The Pnei Yehoshua writes that there is only one Pasuk for both Shen and Regel, since one can be learned from the other ("Shekulim Hem"), as the Gemara concluded on 3a. The other Pasuk only teaches "Lo Mechalya Karna". Therefore the Gemara cannot ask "why was this extra Pasuk written" about Shen (or Regel).

But if you look over what I answered to the first question, you will find that it answers this question as well.

Be well,

-Mordecai Kornfeld

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2) DERIVING ALL OF THE "NEZIKIN" THROUGH A "TZAD HA'SHAVEH"

QUESTIONS: Rava teaches that all of the Avos Nezikin mentioned in the Mishnah, except for Keren, can be derived through a "Tzad ha'Shaveh" from Bor together with any one of the other Nezikin. From Keren together with Bor, all of the Nezikin can be derived. RASHI explains exactly how Shen, Regel, Esh, and Adam are derived through a Tzad ha'Shaveh when one of the other Nezikin is combined with Bor.

There are a number of conspicuous omissions from Rashi's lengthy explanation.

First, when Rashi shows how the Nezikin are derived from Keren and Bor, he explains how Shen, Regel, and Esh are derived, but he does not address Adam. (RASHASH, LECHEM ABIRIM)

Second, although Rashi explains how a Tzad ha'Shaveh can be made from Bor and Keren, from Bor and Shen, from Bor and Regel, and from Bor and Esh, Rashi does not explain how the Tzad ha'Shaveh can be made from Bor and Adam. Why does he omit this?

ANSWER: TOSFOS (DH Ki Shadis) asks how can a Tzad ha'Shaveh can be made from Bor and Adam. None of the Nezikin should be able to be derived from Bor and Adam, because of the Pircha that Bor and Adam are "Ma'asav Garmu Lo" (Bor is considered "Ma'asav Garmu Lo," meaning the damage caused by the Bor is considered a direct result of the owner's actions, as the Gemara says on 6a, and, obviously, damage caused by Adam ha'Mazik is a direct result of the Adam's actions). Although Tosfos answers this question, it seems that Rashi does not accept his answer, and therefore he explains that our Sugya is not relating to Adam at all. Rava is referring only to the Nezikin mentioned in the Mishnah, and he apparently holds like Shmuel who asserts that Adam is not included in our Mishnah. Therefore, Rashi mentions Adam only when he could easily insert it, by including it in a single word (such as by saying that "Adam, too," is derived from the Tzad ha'Shaveh of Bor together with Shen or Regel). Rashi does this in order to explain why the Gemara finds it necessary to point out why Adam was written in the verse (to teach the four payments for damage that he incurs -- Tza'ar, Ripuy, Sheves, and Boshes), implying that Adam could have been learned from a Tzad ha'Shaveh (and was only written explicitly to teach the four payments). However, when he explains how the Nezikin are derived from Bor and Keren, he deals with each one at length, and therefore he does not address Adam. Also, when he explains the Tzad ha'Shaveh between Bor and each of the Nezikin, he discusses each of them at length, and, therefore, he does not discuss the Tzad ha'Shaveh between Adam and Bor.

This is also evident from Rashi's words later (DH Liftor Bo), where he explains that one is exempt from damage done by his Esh to items that were hidden ("Tamun"), which is not true of "Shor, Bor, and Mav'eh." Rashi addresses only the Nezikin of the Mishnah and he does not mention Adam, and he even refers to Shen as "Mav'eh," since that is the word which the Mishnah uses.

This is also why Rashi adds a special comment (on the words, "Adam, l'Chayvo b'Arba'ah Devarim") saying, "Adam -- this is why the Torah wrote it." Rashi's words seem to be unnecessary. In fact, he adds no such comment to the Gemara's earlier discussion of Keren, Shen, Regel, and Bor!

According to what we have explained, though, Rashi's intention is clear. The Gemara should not have discussed Adam, since it is not one of the Nezikin mentioned in our Mishnah. Rashi therefore must point out that, nevertheless, the Gemara must give a reason to explain why Adam is written in the verse, since it can be derived from a Tzad ha'Shaveh, just like the other Nezikin that are listed in our Mishnah.

If Rava is discussing only the Nezikin that are included in the Mishnah according to the opinion of Shmuel, then why does he discuss Keren ? In the Gemara earlier (4a), Rava himself says that Keren is not included in our Mishnah, but rather the end of the Mishnah (9b) alludes to it (see Rashi there). If Rava here is addressing even the Avos Nezikin mentioned in later Mishnayos, then he should address Adam as well, since Adam is mentioned in the Mishnah later (15b)!

It seems that according to Rashi, Rava here is following Rav Yehudah's interpretation (3b) of the Mishnah. Rav Yehudah explains that according to Shmuel, "Shor" refers to Keren, and "Mav'eh" refers to Shen. Therefore, Keren is included in our Mishnah. (See PNEI YEHOSHUA)

This, however, creates two other problems. First, Rava himself rejects Rav Yehudah's explanation, because, according to Rav Yehudah, the Mishnah omits Regel for no reason. Second, why does Rashi address the Mazik of Regel any more than the Mazik of Adam, if neither of them is discussed in the Mishnah?

The answer to these questions might be found in the Yerushalmi. According to the Yerushalmi (cited by the Rashba on 2b), the third Mazik in the Mishnah is learned from the verse, "Ki Yav'er Ish Sadeh" (Shemos 22:4). What hint is there in that verse to the word, "Mav'eh?" It is clear that the proper Girsa in the Yerushalmi is that of the RAMBAM (Minyan ha'Mitzvos, beginning of Nizkei Mamon), whose rendition of our Mishnah reads "Mav'er" instead of "Mav'eh." The word "Mav'er" refers to both Shen and Regel, which are mentioned in the verse, "Ki Yav'er Ish." This is clearly not the Girsa of our Gemara (as is evident from the lengthy discussion on 3b about what "Mav'eh" means). Perhaps Rava in our Sugya was explaining the Mishnah according to the Girsa of "Mav'er." Since "Mav'er" can refer to either Shen or Regel (or both), which are both mentioned in the verse that starts "Ki Yav'er...," there is no reason to reject Rav Yehudah's explanation of our Mishnah. "Shor" refers to Keren, and "Mav'er" refers to both the Nezikin of Shor and Regel. (Even according to our Girsa, "Mav'eh" might be equivalent to "Mav'er," since the guttural letters "Reish" and "Heh" are interchangeable.)

If this is true, we may glean a new understanding in another comment of Rashi. Rashi (beginning of 5b) writes that if the Torah would have written only Shor and Mav'eh, then when pointing out that Keren is "Kavanaso l'Hazik," we would counter that "Shen Tochi'ach," and when pointing out that Shen is "Hana'ah l'Hezeko," we would counter that "Keren Yochi'ach." Rashi, though, is translating "Shor" as Keren, and "Mav'eh" as Shen. This follows neither the opinion of Rav (who says that "Shor" is Keren, Shen, and Regel), nor the opinion of Shmuel (who says that "Shor" is Regel, according to Rava on 4a, and Rashi is explaining Rava's statement here)! (MAHARAM SHIF, NETZIV, RASHASH)

According to the way we have explained, Rashi's words fit perfectly. In our Sugya, Rava is clearly explaining that "Shor" in the Mishnah is Keren, and "Mav'eh" in the Mishnah is Shen (and perhaps Regel as well).

This also explains the words of Rashi earlier (2a, DH ha'Shor v'ha'Bor), where he writes that the order of Nezikin in the Mishnah follows the order in which they are written in the Torah. However, as Tosfos (DH ha'Shor) points out, according to Rav and according to Rava's interpretation of Shmuel, the Nezikin listed in the Mishnah do not follow the order of the verses at all! Based on what we have explained, it is clear that Rashi is following the opinion of Rav Yehudah, since that is the opinion that Rava himself eventually favors, and according to that opinion the Nezikin are indeed listed in exactly the same order as they appear in the verses in the Torah. (M. Kornfeld)