From where do we know that animals that possess neither of the two Simanei Taharah are also subject to the Isur?
Rashi (from Sifra): We learn it with a Kal va'Chomer from those that possess one Siman. 1
Ramban, Moshav Zekenim: From the fact that the Torah writes in Pasuk 5 "u'Farsah Lo Yafris" and in Pasuk 7 "v'Hu Geirah lo Yigar", we learn that all animals that neither possess cloven hoofs nor chew their cud are included in the Lav of "mi'Besaram Lo Socheilu". 2
Why does the Torah write specifically "mi'Besaram"?
Rashi: To preclude the bones, the sinews, the horns and the hoofs from the prohibition.
How will we reconcile this Pasuk, which forbids a Yisrael from touching a Neveilah, with the Pasuk in (21:1), which confines the Isur (of Tum'as Meis) to Kohanim (all the more so, Tum'as Neveilah is permitted to Yisraelim)? And Pasuk 24 "ul'Eleh Titama'u" (implies that it is a Mitzvah to become Tamei through a Neveilah)!
Ramban, Moshav Zekenim: It optional to become Tamei through a Neveilah. Our verse merely teaches that one cannot touch a Neveilah without becoming Tamei, and subsequently he may not enter the Beis-ha'Mikdash or eat Kodshim. 3
Rashbam: The current Pasuk is speaking about someone who wants to touch or eat Kodesh. 4
Sifsei Chachamim: This is he can bring Olas Re'iyah to the Mikdash. (He can touch a Neveilah, immerse, and he is fully Tahor at night! L'Chatchilah he should bring on the first day. Perhaps he should not touch the entire Regel, so he can eat Shalmei Simchah every day! - PF)
Ramban: By the same token, the Toras Kohanim cited by Rashi (Refer to 11:8:3:1*) is not a Lav against touching Neveilah per se. It is either a warning not to do so if one intends to go to Yerushalayim during the Regel, or an Asmachta (since the Mitzvah of remaining Tahor during the Regel is mid'Rabanan.
And how will we reconcile this Pasuk (which prohibits touching a Neveilah) with Pasuk 24 "u'le'Eileh Titama'u" (which declares it a Mitzvah):
Ramban: The combination of the two lead to the conclusion that rendering oneself Tamei by touching a Neveilah is R'shus (permitted).
Since the Torah forbids touching the Neveilah of a Tamei animal, why must it forbid eating it? If he cannot touch it, how can he eat it?! Also, "la'Ger
Bechor Shor: The Isur to touch is only during the Regel. The Isur to eat applies always.
Bechor Shor (Devarim 14:8): The Torah forbids touching in order to eat it.
Refer to 11:8:3:2,3.
One could eat via a Kli, or someone else can put the Neveilah in his mouth, and it will not be Metamei him. 1 And even if Titenenah implies from hand to hand, if forced, we can say that it is not from hand to hand! (PF)
Presumably, there is no Isur to touch if one is already Tamei. (PF) 2