(Mishnah): If Reuven brought his flock into a Dir (a fenced off area for animals to fertilize the land) and locked in front of them properly; and they got out and damaged, he is exempt;

If he locked in front of them improperly and they went out and damaged, he is liable.

If the wall broke at night, or if thieves broke it and an animal went out and damaged, he (and the thieves) are exempt.

If thieves took it out [and it damaged], the thieves are liable.

(Gemara - R. La citing R. Yanai): Tana'im argue about our Mishnah. (Shen and Regel are always Mu'ad. Our Mishnah is like R. Yehudah, who says that a minimal guarding suffices for a Mu'ad. It is unlike R. Meir, who requires first-rate Shemirah for a Mu'ad.)

(R. Lazar): All agree to it.

(R. La): Presumably, R. Lazar is correct. Shemirah was written only regarding Keren. (There is no source for R. Meir to require first-rate Shemirah for Shen and Regel.)

Question: What was the conclusion?

Answer: Reish Lakish says that Tana'im argue about it. R. Lazar says that all agree to it.

Some say that our Mishnah is like R. Eliezer ben Yakov, who says that whether [it is Tam] or [Mu'ad, if he did a minimal guarding] he is exempt.

Question: This is when it was fenced in [all] four directions. If it was fenced in three directions and open in one direction, and it went out from a fenced side [and damaged], what is the law? (He was negligent to leave one side open, but in the end there was Ones not due to the negligence.)

Answer: We learn from the following [Tosefta]. If the wall fell due to the noise of Zo'os (earthquakes or great winds) or the noise of thunder, if he [initially] built it properly, he is exempt. If not, he is liable;

This is needed only when the three stronger walls fell. (Even if also the fourth was strong, it would have fallen, so the Ones is not due to the negligence, and even so he is liable for his negligence! We explained this like NO'AM YERUSHALMI.)