1. The Mishnah discusses the law in the case of a person who did not show his firstborn animal to an expert, slaughtered it, and sold its meat (unbeknownst to his customers).
2. The law (in #1 above) is different when the customers in turn sold the meat to Nochrim or gave it to their dogs.
3. The Gemara discusses the types of blemishes that are significant for a firstborn animal.
4. There is a discussion about how large a hole in the ear must be for it to be considered a blemish.
5. How much of the spine must be lacking in order that the body no longer cause Tum'as Ohel?
6. How much of the skull must be lacking in order that the body no longer cause Tum'as Ohel?
A BIT MORE
1. The seller penalized by having to return all of the money to the customers. For whatever they ate already, they are not liable, and whatever they did not eat should be buried.
2. Since they used the meat only for purposes for which one uses cheap meat, the seller must pay only the value of cheap meat.
3. The criteria for a significant Mum are essentially derived from a Klal ("Ki Yiheyeh Vo Mum") u'Frat ("Pise'ach O Iver") u'Chlal ("Kol Mum Ra"). Just as a broken leg and blindness are blemishes that can be seen and that do not heal, all blemishes that can be seen and do not heal are considered blemishes.
4. The Gemara notes that it is possible that a smaller size may disqualify the animal from being offered as a Korban, while a larger size may be required to allow it to be slaughtered by the Kohen.
5. Beis Shamai: Two vertebrae. Beis Hillel: One vertebra.
6. Beis Shamai: The size of the hole made by a Makde'ach (drill). Beis Hillel: Enough that if it would be taken from a live person, he would die.