Bava Kamma, Chapter 5, Mishnah 6, deals with a pit of two partners - a jointly owned pit. The basic rule is that the partners are jointly responsible for it, and they must share the damage payments. It makes no difference whether the pit is located in the public domain - such as if they dug it together to a depth of ten handbreadths - or in a private domain, such as if they owned a field with a pit in it, and they jointly declared the area around it ownerless. In all these cases, the responsibility falls on both of them.
The situations in which only one of the partners is liable:
"Avar hadoleh harishon velo chissahu" - the first one finished drawing water from the pit, and as the Gemara explains, he handed his partner the cover or the bucket and said to him: I have finished, it is handed over to you and you may use it. By doing so, he made the second partner the guardian of the pit, and the responsibility passed entirely to him. Therefore, "Hasheni velo chissahu - hasheni chayav": if the second partner did not cover the pit properly after using it and damage occurred, he alone is liable, not the first.
"Chissahu harishon uva hasheni umatza'u megulleh velo chissahu - hasheni chayav" - the first partner covered the pit properly and legally, but over time the cover became worm-eaten or damaged, and the pit became dangerous. The second partner found it uncovered or improperly covered and did not cover it - and only he is liable, since the first partner was a victim of circumstances beyond his control and knew nothing of the mishap. If the second partner had informed him that the cover rotted and needed to be fixed, and there was enough time for the first one to arrive - he too would be liable. But when he did not know or did not have time to arrive, he is exempt, and the responsibility falls entirely on the second partner.
"Chissahu kara'ui":
The meaning of "properly" is a cover that can be expected to stay in place indefinitely, according to the normal traffic conditions in the area. This does not mean that the pit will never, even in the distant future, become exposed; rather, the verse that speaks of covering the pit does not require sealing it by refilling it with dirt, and a person may leave it as a hole in the ground as long as he covers it properly. Therefore, one who covered it in a way that the cover can withstand normal traffic conditions, "Venafal letocho shor o chamor vames - patur", since he did what was required of him and he is a victim of circumstances beyond his control.
"Lo chissahu kara'ui" - here it does not necessarily refer to partners, but to any person who did not cover his pit properly. The verses mention donkeys and cows falling into a pit, but the Gemara's premise is that in a place where heavier animals, such as camels, pass through, there is an obligation to prepare a cover that will withstand not only normal donkeys and cattle but even a camel. This is because camels are heavier, and if they step on the cover it will wear down, and eventually a donkey will fall into it and break it, after the weight of the camel weakened the cover.
In the period of the Mishnah and Gemara, camels weighed more than cows, which is not the case today. For a long time, cows were selectively bred so that they would grow larger and produce more meat, and therefore cows today are much heavier than a typical dromedary camel. Even in the 1970s, a yearling cow weighed about ninety-six pounds less than its weight fifty years later; cows are continually improving, and today a cow might weigh about a thousand kilograms, whereas in the time of the Mishnah it weighed about five hundred kilograms compared to a camel that weighed about six hundred. The point that emerges from here is that there is an obligation to cover the pit in a way that will withstand the load of the traffic passing through the area, even if it only passes there occasionally, and whoever fails to do so is liable.
An animal that fell due to the sound of digging:
Reuven dug a pit in the public domain - thereby already acting unlawfully - and hired a worker to perform labor in it, such as widening it with a jackhammer so it would hold more water. Shimon passes by the place with his animal, and the sound of the digging frightens it. In this regard, the Mishnah distinguishes between two situations:
"Nafelah lefanav mikol hacheriyyah - chayav" - the animal was frightened by the sound of the digging and fell forward into the pit. The one liable is not the person performing the labor, but the owner of the pit, Reuven who dug it, and he is fully responsible. The worker operating the jackhammer is merely in the category of indirect causation (gerama) - he indirectly caused the animal's fall, and one who causes indirect damage is exempt. The owner of the pit, however, created a public hazard, and therefore he pays for all the damage.
"Le'acharav mikol hacheriyyah - patur" - it is easy to mistakenly understand this law. The meaning is that the animal reached the edge of the pit, was startled by the noise coming from inside it, and fell backward - not into the pit but onto the ground beside it. In this case, everyone is exempt, both the one who dug the pit and the one performing labor in it now, since what ultimately struck the animal was the ground of the public domain, and this is no one's fault. Even though the worker frightened it with the jackhammer, this is only indirect causation (gerama), and he is exempt.
For what the owner of the pit is liable and for what he is exempt:
The verse uses two examples - an ox and a donkey - and the Gemara deduces: one animal would have been enough, so why were two mentioned? To teach us:
"Shor" - an ox, and not a human: There is no liability for a human who dies in a pit.
"Chamor" - a donkey, and not vessels: There is no liability for the vessels on the donkey, such as the saddle, the saddlebag, the plow, and similar items.
This is what the Mishnah says: "Nafal letocho shor vekeilim venishbaru, chamor vekeilav venikre'u - chayav al habehemah ufatur al hakeilim" - if an ox and vessels fell into it and broke, or a donkey and its vessels and they tore, he is liable for the animal and exempt for the vessels. If an ox fell into a pit with a yoke or plow on it, and the animal died or was injured, and the plow or yoke also broke; or similarly, if a donkey fell into a pit with a saddlebag on it and it tore - the digger pays compensation for the death or injury of the animal, but is exempt for the vessels, the yoke, the saddle, and the objects, based on the derivation from the verse.
"Nafal letocho shor cheresh, shoteh vekatan" - if a deaf, deranged, or small ox fell into it:
The owner of the pit is not liable for every ox. The Mishnah is speaking of an ox that is somewhat impaired, which is not equipped to deal with the dangers of an environment that has pits: deaf or blind; deranged - a crazy ox; and small - an ox that has not yet learned how to conduct itself, to plow, and so forth. The digger is liable for these animals, since it was injured or died because of him. However, from a precise reading of the Mishnah's language, it emerges that if it is a whole, healthy, and mature ox that wanders and falls into the pit and gets hurt - the owner of the pit is considered a victim of unavoidable circumstances and is exempt, since the ox should have been careful, and it is not the way of oxen to walk into pits and fall into them.
However, when the animal has a good reason why it did not know where it was going - such as being deaf, deranged, or small, an impaired animal or one lacking intelligence, or if the incident happened at night and it could not see where it was stepping, or if he placed a defective cover that created a sort of trap for it - even if a healthy animal fell, the digger is completely liable. This is because there is no room to claim unavoidable circumstances: how could the animal protect itself from falling in the dark or from a trap that was set for it?
"Ben o bas, eved o amah - patur" - if a son or daughter, a slave or maidservant fell in, he is exempt:
Since we learned that one is exempt for damage to a human being, there was room to ask what the law is regarding minors who lack intelligence. The Mishnah replies that there is no practical difference even if a boy or girl fell into the pit: even though from a halachic perspective they lack intelligence, by virtue of the derivation from the verse, which comes to exclude human beings, he is exempt for them. The same law applies to a slave and a maidservant. Even though derivations sometimes compare slaves to animals, and even though the slave is the property of his master, this matters not at all: as long as a human being fell into the pit, and even if he was blind and could not have known, by virtue of the derivation from the verse, the owner of the pit is exempt.
In conclusion, it is worth noting an interesting dispute: was the exemption for an animal that should have been careful stated specifically when the animal dies, or even when it is only injured? The Shulchan Aruch rules that the exemption applies only to the death of the animal, but if it was only injured - such as if it twisted its leg - the digger is liable to compensate its owner, since this is the nature of pits, and the exemption is stated only regarding death. However, the Rema rules in accordance with the second opinion, according to which one is completely exempt even if an animal that should have been careful entered the pit he dug and twisted its leg in it.