Abba Channan says in the name of R. Eliezer: The shesuah is a beast in itself; it has two backs and two spines.
R. Yashiah said: Wherever "tzippor" is written, a clean bird is intended.
R. Yitzchak said: A clean bird is called either "of" or "tzippor"; an unclean bird is called only "of."
(Devarim 14:3) "You shall not eat any abomination": R. Eliezer says: Whence is it derived that if one slit the ear of a bechor (a first-born beast, thus blemishing it) and ate of it (the beast, after slaughtering it), he transgresses a negative commandment? From "You shall not eat any abomination."