The introductory Mishna to Massekhet Bava Kamma offers the four avot nezikin. While avot translates literally to “fathers,” the term in this context refers to the primary types of damages according to the Torah: – Shor (an ox), Bor (a pit), Mav’eh and Hev’er (fire) – each with its own set of rules.
Of these four archetypes of damage, two are clear. A Bor is a pit that is dug in a place where someone or someone’s property can fall in and become injured or damaged. Hev’er is fire that destroys property. The other two cases – Shor and Mav’eh – need further explanation; Rav and Shmuel argue in the Gemara about how to define them. Shor clearly means damage done by an ox, but an ox can do damage in a number of different ways and it is not clear what types of damage the term Shor refers to.
According to Rav, the Mishna has listed the four types of damages that appear in the Torah, and Shor is a broad term that encompasses keren (damage done with the animal’s horns), shen (damage done with the animal’s teeth, i.e. eating) and regel (damage done by the animal’s hooves while walking). Mav’eh refers to a different type of damage mentioned in the Torah – a person who does damage. Shmuel believes that the Mishna is listing only those avot nezikin that are damage done by property that the owner should have expected. Thus Shor refers specifically to damage done by the animal while walking (regel) while Mav’eh refers to damage done by the animal when it eats (shen). According to Shmuel, the Mishna does not deal with a person who does damage, as it is a different category of damage.
The Talmud Yerushalmi explains that Shor means keren and Mav’eh includes both shen and regel. Thus, according to the Yerushalmi, the Mishna includes all cases of damage done by someone’s property.