(Mishnah): There are four Avos Nezikin (primary categories of damagers): an ox, a pit, Mav'eh (explained below), and fire.

Re'i of an ox is unlike that of Mav'eh, and vice- versa. (Usually, Re'i refers to a stringency. Initially, the Gemara understands that here it refers to a leniency.)

Re'i of these two, which are alive, is unlike that of fire, which is not;

Re'i of these three, which move and damage, is unlike that of a pit, which does not;

The common side of all four is that their nature is to damage, and you are obligated to guard them. If they damaged, the damager must pay from Meitav (highest quality land).

(Gemara) Inference: If these are Avos, there must be Toldos (offshoots).

Question: Are the Toldos like the Avos, or not?

(Mishnah): (Regarding Shabbos) there are 39 Avos Melachos. The Toldos are like the Avos;

The punishment for either is stoning (if Mezid) or a Korban Chatas (if Shogeg).

Question: What difference does it make if they are Avos or Toldos?

Answer: If someone did two Avos or two Toldos (of different Melachos, b'Shogeg), he brings two Chata'os;

If he did an Av and a Toldah of that same Melachah, he only brings one Korban.

Question: R. Eliezer says that in all cases, he brings a Korban for every Melachah. How does he explain the difference between Avos and Toldos?

Answer: Those that were done in the Mishkan are important, so they are called Avos. The others are less important, so they are called Toldos.

(Mishnah): Avos ha'Tum'ah (include) Sheratzim (rodents), semen, and one who became Tamei through a corpse.

The Tum'os are unlike the Avos. An Av ha'Tum'ah is Metamei people and Kelim. A Toldah does not.

Answer (Rav Papa): Regarding Nezikin, some Toldos are like the Avos, and others are not.

(Beraisa): Three Avos pertain to an ox: Keren (the horn, i.e. goring), Shen (eating) and Regel (trampling).

Question: What is the source for Keren?

Answer (Beraisa): "If an ox will gore" - goring is with the horns.

We learn from "he made for him... horns... 'with these you will gore Aram'" and "... his horns, with them he will gore nations".

Question: Why is a second verse needed?

Answer #1: If you will say that mid'Oraisa laws are not learned from Nevi'im, we can learn from a verse of the Torah.

Objection: We are not learning a law. We just clarify that goring is with a Keren!

Answer #2: Rather, one might have thought that the Torah distinguishes between a Mu'ad (an animal established to gore) and a Tam regarding detached horns, but if the horns are attached, it is always considered Mu'ad;

"His horns..." teaches that this is not so. (It calls goring with attached horns 'Negichah', the same word used to discuss a Tam or Mu'ad that gored.)

Question: What are the Toldos of Keren?

Answer: They are pushing, biting, crouching and kicking.

Question: Why is only goring an Av?

Suggestion: It is because it says "if (an ox) will gore..." 2. Rejection: It also says "if will push"!

Answer: The latter verse also refers to goring.

(Beraisa): The Torah first says "Yigach (gore)" and later "Yigof" to teach that both are the same.

Question: Why does it say "Yigach" regarding goring people and "Yigof" regarding goring animals?

Answer: Man has Mazal (understanding to guard himself; alternatively, an angel that advocates for him), so it says "Yigach" (he would not be gored unless the animal intended). Animals lack Mazal, so it says "Yigof" (it could be gored without intent).

This teaches that an animal Mu'ad to gore people is (also) Mu'ad to gore animals, but not vice-versa.

Question: Why is biting a Toldah of Keren? It is a Toldah of Shen (eating)!

Answer: No. Shen is when the animal has Hana'ah (benefit or pleasure). The animal gets no Hana'ah from biting.

Question: Why are crouching and kicking Toldos of Keren? They are Toldos of Regel (trampling)!

Answer: No. Regel is common damage. Crouching and kicking are not common.

Question: Rav Papa said that some Toldos are unlike the Avos. To which did he refer?

He cannot refer to these Toldos of Keren. Keren has intent to damage, it is your property, and you are responsible to watch it. The same applies to these Toldos!

Answer #1: Rather, the Toldos of Keren are like Keren. Toldos of Shen and Regel are unlike those Avos.

(Beraisa): "He will send" refers to Regel - "sending the Regel of oxen and donkeys."

"And it will consume" refers to Shen - "like the Galal (tooth) will consume"