The first sentence in Mishnah 8 summarizes the topic we have been dealing with in the recent Mishnayos: the right of a worker to eat from the food he is working with during his labor.
"Shomrei peiros" - We are talking about people who do no work with the fruit at all, but merely stand and guard them, like a sort of human scarecrow. The fruit themselves are at a stage where those working with them are permitted to eat from them by virtue of the right the Torah granted them - after detachment and before the completion of work. But since the guards do not perform work with them, they have no permission to eat from them by Torah law.
"Ochlin mehilchos medinah, af al pi she'ein zeh min haTorah" - their permission to eat does not stem from a Torah right, but rather from local custom: the prevalent custom of workers, that even a guard is permitted to eat. At that time and place this was the accepted custom, as the mutual interest is that the workers' satisfaction be maintained, and a person is expected to work according to customary conditions. With this, the topic concludes.
The Four Watchmen:
From here on, the Mishnah opens an entirely new topic - not just a new paragraph or even just a new Mishnah, but almost a new chapter. We return to the topic discussed in the third chapter: the laws of the four watchmen and accepting deposits, and later in the chapter - the concept of guarding in general. We are talking about a person who is asked to bear responsibility for someone else's property.
The Mishnah says: "Arbaah shomrim hem" - there are four types of watchmen:
Shomer chinam - an unpaid watchman, who does a favor for the owner and guards the property without compensation.
Shoel - a borrower, where the owner does the favor for him; he receives all the benefit, and does not lose or pay anything.
Nosei sachar - a paid watchman, who receives payment for his guarding, also called a shomer sachar.
Socher - a renter.
The latter two, nosei sachar and socher, are engaged in an arrangement of give and take: the paid watchman receives payment for guarding the flock, while the flock's owner receives the benefit of the guarding. Similarly, the renter: on one hand, he receives the right to use the object, and on the other hand, he pays rent to its owner - so both sides receive.
Three Levels of Liability:
Peshiah - negligence, as well as intentional damage. Negligence is a passive failure, such as not locking the door properly; while intentional damage means he actively did a bad act to the object deposited in his hands. All watchmen are liable at this level, even a shomer chinam, since he is expected at the very least to be a reasonable watchman and not act with negligence.
Geneivah va'aveidah - theft and loss, things that are preventable with a certain amount of effort. The nosei sachar and socher are liable for these, while a shomer chinam is exempt.
Onasin - uncontrollable circumstances that are beyond a person's control. A nosei sachar and a socher are exempt for these, while a shoel is liable.
A shomer chinam is exempt for loss and theft, because he did not commit to investing great effort to prevent such cases, and he acted in good faith. Although he is exempt from paying, a series of oaths is imposed upon him: he must swear in Beis Din that he was not negligent, that things happened as he reports, and that he did not misappropriate the objects he was meant to guard. The rule is: he does not pay as long as he swears, for everything besides peshiah.
In contrast, a shomer sachar and a socher are liable for theft and loss. They are expected to invest extra effort in guarding the object, since they receive compensation for it; therefore, if something happens that they could have reasonably prevented, they must pay.
In cases of unavoidable accidents, on the other hand, a paid watchman and a renter are exempt. If the animal dies suddenly - it is not the watchman's fault, there was no negligence here, and he could not be expected to guard it any better. Here too, he must swear an oath to exempt himself in the relevant matters.
The borrower, unlike all the others, is liable even for unavoidable accidents. Since he receives all the benefit, even though it is not his fault that something bad happened to the animal, he must pay and compensate; for the owner who lent it essentially tells him: "I do not care what happened, you must return what is mine." This is the obligation of a borrower, and these are the three levels.
The text of the Mishnah:
"Shomer chinam nishba al hakol" - he swears and is exempt not only for theft and loss, but even for unavoidable accidents.
"Vehasho'el meshalem et hakol" - the borrower pays for everything, even for unavoidable accidents.
"Nosei sachar vehasocher nishba'in al hashevurah ve'al hashevuyah ve'al hametah, umeshalmin et ha'aveidah ve'et hageneivah" - the first three cases are examples of unavoidable accidents, things that are out of their control, and for them an oath is sufficient; whereas for loss and theft they must compensate the owner, since they could have watched it better.
Examples of unavoidable accidents:
"Hashevurah" - that it was fractured, such as an animal that broke its leg.
"Hashevuyah" - that it was captured, quite literally. Regarding an animal, the meaning is that armed robbers came, or even a single robber, who put a weapon to the shepherd's head and demanded: "Give us the sheep." This is an unavoidable accident and the watchman is exempt. This is not similar to theft, which is done secretly at night while the watchman is asleep; rather, when the act is done by force, it is called captured, or armed robbery.
"Hametah" - death due to natural causes: the animal died suddenly or due to old age. This too is included in the category of unavoidable accidents, and therefore a paid watchman and a renter are exempt - unlike a borrower, who is liable even for such things.
In summary: In the reisha we learned that watchmen of produce may eat by the custom of the land and not by Torah law, since they are not performing a physical task. From here we opened a new topic - four watchmen: an unpaid watchman, a borrower, a paid watchman, and a renter, and the three levels of liability among them: negligence, for which everyone is liable; theft and loss, for which a paid watchman and a renter are liable but an unpaid watchman is exempt; and unavoidable accidents - fractured, captured, and dead - for which everyone is exempt with an oath, except for the borrower, who pays for everything.