Chapter 3! A focus on the slaughtering of kosher animals -- and what makes an animal kosher (as compared to a treyfa, which is a kosher kind of animal, but some blemish prevents it from being kosher upon shechitah). Which is to say: a new mishnah -- that lists 18 "defects" that make an animal a treyfa in detail - and then because of the animal's status, the shechitah cannot be kosher. Plus, what is the source in the Torah for this concern about a treyfa? That should be obvious - it's an explicit verse, but what about the position that a treyfa has to be an animal that won't live from the defect? That source is provided - Leviticus 11. Also, the Gemara adds another 7 ways an animal could become a treyfa. With a mnemonic to remember them -- and a strong question why they weren't included in the 18.