Bava Kamma, Chapter 4, Mishnah 4. This Mishnah discusses payments for damages in a case where one of the involved parties lacks legal competence - a cheresh, a shoteh, or a katan.
These three who lack legal competence:
Cheresh - a deaf-mute from birth, who can neither receive nor communicate information. We therefore assume that he lacks competence, meaning he is unable to understand the consequences of his actions.
Shoteh - a person who lacks mental capacity. He performs actions that endanger himself or damage his own property, and he too does not understand the consequences of his actions.
Katan - a minor, a boy or girl before the age of bar mitzvah or bas mitzvah. Since they have not developed to the stage where they fully understand consequences, they are not legally responsible for a variety of matters, including monetary liability when their property causes damage.
Regarding minors, this usually involves orphans who inherited a cow from their father, and now it is causing damage. Are they obligated to pay? The answer is no. The foundation of all these Mishnayos, of the entire tractate, and of the entire Order, is that a person must take responsibility; and since they are not expected to bear responsibility, they cannot bear it. If they were responsible, they would be obligated to compensate and pay, but since we do not impose responsibility upon them, they do not pay.
The law of the Mishnah - a competent person versus a cheresh, shoteh, and katan:
"Shor shel pike'ach shenagach shor shel cheresh, shoteh vekatan - chayav" - a competent, normal, healthy, and legally responsible person whose ox gored the ox of a cheresh, shoteh, or katan is liable for damages, as the responsibility is placed upon him to ensure his animal does not cause damage. Even though the injured party lacks legal competence, the damager must pay.
"Veshel cheresh, shoteh vekatan shenagach shor shel pike'ach - patur" - if an animal belonging to a cheresh, shoteh, or katan damaged a healthy, legally competent person, its owners are exempt from payment. Regarding this, it is said elsewhere "a bad encounter": one who enters a confrontation with them ends up losing, as he must pay them, whereas they do not have to pay him, because they lack legal competence.
"Shor shel cheresh, shoteh vekatan shenagach - beis din maamidin lahen apotropos":
When an animal belonging to a cheresh, shoteh, or katan causes damage - and the term "gored" here is flexible, as it does not mean the ox is already a muad (forewarned), but rather that it gores and causes trouble - its owners cannot be brought to court, since they lack legal competence: they cannot be warned, and their animal cannot be made a muad. Therefore, the beis din appoints a guardian for them, a sort of watchman and trustee, to supervise and ensure that the animal does not cause damage, for the benefit of the public.
Although it is highly likely that the beis din has already appointed a guardian for the cheresh, shoteh, and katan, since they need a legal representative, this representative is there solely for the benefit of the minor or the orphan. He is not appointed to be summoned to court regarding the guarding of animals, since that is not to their benefit. Their benefit is that they bear no responsibility at all: they keep their animal and do not pay for damages. However, once it becomes clear that the animal causes damage, a person is appointed for this purpose - whether an additional person or assigning an additional role to the existing guardian - who bears the responsibility and serves as an address for compensation claims.
"Umei'idin lahen bifnei ha'apotropos" - if the animal gored additional times, the injured parties can bring the guardian to court and warn him that the animal causes damage, and after three times it becomes a muad. Then the payments increase from half damages to full damages: until now there was no payment at all, whereas once it becomes a muad, payments apply for which the children are responsible.
There is a dispute as to how this is done: whether the guardian takes the money from the children's assets, or whether he pays out of pocket and receives a reimbursement from them. Either way, it is clear that he does not bear direct financial responsibility, for if that were the case, he would not have agreed to serve as a guardian in the first place, and that is not what we want. We want someone who will take responsibility for keeping the streets safe, and therefore we do not impose on him more than to do his best and serve as an address for complaints.
"Nispake'ach hacheresh, nishtapah hashoteh, vehigdil hakatan":
The Mishnah continues and lists three changes: "Nitpake'ach hacheiresh" - the deaf-mute was cured and can now hear and speak; "nishtapah hashoteh" - the mentally incompetent person regained his sanity and was cured; "vehigdil hakatan" - the minor reached the age of bar mitzvah. What is the law of the ox from now on?
"Chazar letumato, divrei Rabbi Meir" - according to Rabbi Meir, the ox reverts to being a tam, and even if it was established as a muad by the guardian, it returns to its tam status. The reason: once the domain changes and the ox is transferred to new owners, its nature and fortune change, and the ox undergoes a sort of reset and reverts to its tam status.
"Rabbi Yosi omer: harei hu bechezkato" - according to Rabbi Yosi, the ox remains a muad just as it was.
According to the simple understanding, the dispute is whether the status of the ox resets upon a change of ownership. The halachah follows Rabbi Yosi. However, the Rambam, as well as the Shulchan Aruch who quotes him, understand that even Rabbi Yosi concedes that in a complete sale, the status of the ox resets. It is only in a case where the owner of the ox was cured and regained his sanity that this is not considered a true change of domain and a new owner, and therefore Rabbi Yosi agrees that the ox remains a muad.
"Shor ha'itztadin" - a new topic:
The final part of the Mishnah deals with a completely separate law: an animal that kills a human being is liable to death by stoning and is actually executed. It makes no difference whether it is a cow, a dog, or a rooster. The rule is that an animal that intentionally kills a person is treated to a certain extent like a human murderer, and it is put to death.
Regarding this, the Mishnah states: "Shor ha'itztadin eino chayav mitah" - an ox trained to perform in a stadium, in the manner of bullfights, is not stoned even if it killed a person. The reason: "Shene'emar: ki yigach" - "If an ox will gore a man," implying that it gored on its own accord, as opposed to "sheyagichuhu", where others incited it to kill.
In other words, if someone trains a cow to be a killer, it is no longer its fault that it attacks people, since he is the one who trained it to do so, and therefore it bears no responsibility. Even if it intentionally attacked a person and killed them, it is not subject to the punishment of stoning, since it is not, so to speak, its fault: the derivation from the verse teaches that if it was trained to be a killer, it is therefore not liable to death.