If a cow slips and falls into a garden and eats the produce or damages the produce when it breaks his fall the owner pays for the amount that he benefited.
If a person willingly saves his friend from a loss if it didn't cost him anything he is regarded as a 'Mavri'ach Ari' and the beneficiary is not obligated to pay.
If an animal was pushed by another animal into a garden it is a Machlokes if it is considered a Peshi'ah and the owner must pay for damages. (1)
R. Kahana holds that if an animal falls into a garden and moves from one furrow into another furrow it is Chayav to pay for damages.
R. Yochanan says that even if it moves from furrow to furrow it only pays for the benefit unless it left the entire field with the knowledge of the owner and returned to the field.
R. Papa explains that if it left the entire field with the knowledge of the owner even if it returned to the field without his knowledge he is Chayav to pay for damages. (2)
It is a Machlokes if a person was negligent at first but at the end the damage occurred by way of an Ones if he is Chayav.
If an animal walks down into someone's garden and causes damage the owner is Chayav.
If an animal walks down into a garden and causes damage with amniotic fluid it is a Safek if the owner is Chayav. (3)
Shen and Regel are Patur in Reshus ha'Rabim.
Rebbi Yosi Bar Chanina says that if an animal damages with Shen a field of 60 Se'ah is evaluated and the value is divided by 60 and we evaluate how much a Beis Se'ah decreases in value as a result of the damage.
R. Yanai says that a field of 30 Se'ah is evaluated and the value is divided by 60 and we evaluate how much a half of a Beis Se'ah decreases in value as a result of the damage.
Chizkiyah says that we evaluate the amount that was damaged in a field that is sixty times the size of that amount. (4)
If an animal cuts down a sapling Rebbi Yosi says that the Gozrei Gezeirah in Yerushalayim decreed that for a one year old sapling two Kesef is paid and for a two year old four Kesef is paid.
If an animal eats unripe grain Rebbi Yosi ha'Glili says that it must pay the amount that the remaining grain is worth after it is fully grown.
The Chachamim say that we evaluate how much the field is worth with and without the unripe grain.
A BIT MORE
1. R. Kahana holds that it is considered a Peshi'ah because he should have had the animals pass by one after the other.
2. Since the animal was in the field once the owner of the animal must be extra vigilant in guarding the animal so that it does not return to the field and if he does not guard it extra vigilantly and it returns to the field he is Chayav.
3. According to the opinion that a person is Chayav if he was negligent at first but at the end the damage occurred by way of an Ones he is definitely Chayav in this case. The question is according to the opinion that he is Patur. Maybe in this case he is Chayav because it is regarded as a complete negligence because since the animal was close to giving birth he should have been extra vigilant in guarding the animal.
4. We evaluate how much a field that is 60 times bigger than the amount that is damaged decreases in value as a result of the damage.
PAYING FOR BENEFIT
If a cow slips and falls into a garden and eats the produce or damages the produce when it breaks his fall the owner pays for the amount that he benefited. The Ketzos ha'Choshen says that a payment for benefit is not the same as a payment for damages. When one pays for damages he must pay from Idiyos (the best of his field), however the payment for a benefit does not come from Idiyos because he is considered a Ba'al Chov not a Mazik and he only pays from Ziburis because a Ba'al Chov pays Min ha'Torah from Ziburis. Even though the Rabanan decreed that a Ba'al Chov pays from Beinonis that only applies when he borrowed money with the Da'as of the lender but in this case he benefited without the Da'as of the owner and therefore he only pays Ziburis.
A DAMAGED GARDEN
An animal that slipped on a stone or on its urine and fell into a garden and fell on the produce and destroyed them or ate the produce it pays for the benefit. Even if it went from furrow to furrow and even if it remained there the entire day it only pays for the benefit. What benefit does it have from falling on the produce? It was protected from breaking its bones. But if it walked down to the garden normally and it ate the produce it pays for what it damaged. Even if it dirtied the produce with amniotic fluid it must pay for the damage because it was negligent in the beginning. So too, if one animal pushes another into the garden it pays for what it damaged because the owner should have allowed the animals to pass one after another. (Shulchan Aruch CM 394:1)