Bava Kamma, Chapter 3, Mishnayos 3 and 4. The Mishnah before us presents an interesting case: what is the law regarding a person whose own body becomes the "bor" in the public domain.
The language of the Mishnah:
"Shenei kaddarin shehayu mehalchin zeh achar zeh" - Two potters, meaning manufacturers of pots, who were walking on the road one after the other. The fact that they are potters is not essential to the story itself.
"Venitkal harishon venafal" - The first person tripped and fell to the ground.
"Venitkal hasheni barishon" - The second person tripped over the body of the first person lying on the road.
"Harishon chayav benizkei sheni" - The first person is liable to pay for the damages caused to the second person.
As we may recall, a few Mishnayos earlier we learned the dispute between Rabbi Meir and Rabbi Yehudah regarding the law of a "nitkal" - a person who tripped on his feet:
According to Rabbi Meir: "Nitkal poshea hu" - the one who trips is considered negligent, and is fully responsible for the results of his fall.
According to Rabbi Yehudah: "Nitkal lav poshea hu" - he is not considered negligent, and therefore is not necessarily responsible for the consequences of the fall.
If we study the Mishnah according to the opinion of Rabbi Meir, the law is simple and self-evident: the first person is liable for the damages of the second, since one who trips is considered negligent. According to this approach, there is no difference between someone who tripped accidentally and someone who deliberately lay down in the middle of the road to trip passersby - they both share the exact same law.
The explanation of the Gemara - The Halachah follows Rabbi Yehudah:
The Gemara establishes the Mishnah according to Rabbi Yehudah, since the Halachah follows his opinion that one who trips is not negligent. Therefore, we must explain why the first person is liable for the damages of the second. After all, it seems to be merely an accident, and a person who acted responsibly and tripped is not liable. We must conclude that this refers to a case where the first person had enough time and ability to get up and remove himself from the road, and he did not do so. Since he lingered in the public domain and did not get up, and then the second person tripped over him, his body functions as a "bor" in the public domain - he turned himself into an obstacle, and therefore he is liable.
Consequently, if he did not have time to get up, for example if he lost consciousness, or if the second person was walking closely behind him and tripped over him immediately after the fall - he is exempt.
Thus, even though the Halachah follows Rabbi Yehudah that one who trips is not negligent, nevertheless, this person is responsible for leaving himself in the public domain as an obstacle, like a "bor", and therefore the second person has a valid claim against him.
The parameters of the liability: "Bor" and not "Adam Hamazik":
We must remember that here we are dealing with the primary category of damage called "bor" - a hazard in the public domain, as opposed to "adam hamazik" (a person who damages). It is not the person himself causing damage through his actions or even his direct force, but rather he is serving as a sort of inanimate object that trips passersby. And as is known, regarding a "bor", the rule is "a donkey and not utensils" - the owner is responsible for damages to a donkey and the like, but not for damages to the victim's utensils. And from here:
Damage to the second person's body: If he was injured in his fall, for example, he sprained his ankle - the first person pays him for his damages.
Damage to the second person's utensils: If he was carrying a pot in his hand and it broke - the first person is exempt from paying for it, just as he would be exempt for breaking a pot in a regular pit that he dug in the public domain.
Payments for a pit versus payments for a person who causes damage:
Another important point: In payments for a pit, the damager pays for the damage alone - the actual damage caused to the victim - and not the five payments. As we briefly mentioned earlier, a person who intentionally injures his fellow pays five payments:
Nezek - the decrease in the person's value, how much he is worth now in the slave market compared to his previous value.
Sheves - the loss of work days.
Ripui - the medical expenses.
Tza'ar - compensation for the physical pain.
Boshes - compensation for the emotional pain.
In our case, only the payment of Nezek is relevant, meaning the decrease in the victim's value, because the four additional payments apply only when the damager acted with some form of negligence. Here we establish that he is not negligent, but rather functions solely in the category of a pit.
In summary: In this Mishnah we learned how a person himself becomes a 'pit' in the public domain. The halachah follows Rabbi Yehudah that one who stumbles is not negligent, and therefore the first person's liability is not for the fall itself, but rather for the fact that he was able to get up and remove himself from the path and did not do so, leaving his body as an obstacle. Since his liability is based on the law of a pit, he pays for the damage to the second person's body but is exempt for his utensils ('a donkey and not utensils'), and even for the bodily damage he only pays the payment of Nezek alone, and not the other four payments of a person who causes damage.