Gemara

12b (Mishnah): One is liable for damage to property to which Me'ilah does not apply.

(Inference): Me'ilah does not apply to them, but they are Kodshim!

(R. Yochanan): The Mishnah discusses Kodshei Kalim. It is like R. Yosi ha'Glili, who says that they are the property of their owner.

17a (Mishnah): If something was tied to a chicken's leg, it pays half-damage.

19b - Question: If it became tied by itself, who pays?!

The owner of the chicken is exempt, for it says "when a man will open a pit", not when an ox will open a pit (create an obstacle).

48b (Mishnah): If an ox fell into a pit and dirtied the water (the owner is liable).

(Rava): This is only when it dirtied the water when it fell. If it dirtied it after it fell, he is exempt.

This is because after falling, the ox is (a stationary damager) like a pit, and the water is like Kelim. A pit is exempt for Kelim.

Question: This is like Shmuel, who says that all obstacles are like a pit. Rav says that they are like a pit only if he makes them Hefker. If not, they are like his ox. Oxen are liable for Kelim!

Retraction (Rava): This is only when its body dirtied the water. If it died in the pit and the rotting carcass imparted a bad smell to the water, he is exempt.

This is because it is mere Gerama (causation).

54a - Question: According to R. Yehudah, who obligates for Kelim, what does "a donkey" come to exclude?

Rava: This is difficult.

Rishonim

Ramban (Kuntres d'Garmi DH Nofal): Rava taught that if it merely gave a bad smell to the water, he is exempt because it is Gerama. We obligate Garmi only for people, but not for animals. The Rif omitted this because Rava explained Rav, but the Rif rules like Shmuel, who says that every Takalah is like a pit. One is exempt for a pit due to an animal. The correct text says that Rava taught this, even though he obligates Garmi. According to this, if an ox made a fire that burned documents or tore them or smudged them, it is exempt, for this is Gerama of the ox. Really, it is liable. It is unlike an ox that fell into water. There; the water becomes smelly automatically. Here, the ox did an act.

Nimukei Yosef (21a DH ha'Rif): The Rif did not bring Rava's law. He holds that Rava taught this because Rava exempts Garmi, but we hold like the opinion that obligates for Garmi. The Ro'oh says in the name of his Rebbi that this is wrong. Garmi applies only to people. All agree that the Torah does not obligate animals for enabling Nezek - "when a man will open a pit", not when an ox will open a pit. The same applies to all Nezikim.

Question (Shach 5): The Ro'oh's Rebbi was the Ramban, and he obligates animals for Garmi! I concluded that Garmi is a fine mid'Rabanan. Chachamim decreed only about common things, therefore one is exempt for an animal.

Kehilas Yakov (Bava Kama 35:2 and Kidushin 28): "When a man will open..." exempts an animal that made a damager. What is the source to exempt for an animal that damaged through Garmi? Garmi is not considered damage, rather, making a damager. E.g. a Moser causes another to steal, one who burns a document enables the borrower to deny... The Ramban holds that Garmi is like damage, but admits that Gerama is only like making a damager. One is liable b'Yedei Shamayim even if his property did it.

Shiltei ha'Giborim (21a-b): My grandfather says that we do not obligate for Gerama of an animal. I say that this is like other Geramos. It is the man's Gerama for bringing his animal there without permission. Letter of the law, he is exempt. However, it is proper to fine him, like for other Geramos.

Poskim

Shulchan Aruch (CM 386:1): We hold like R. Meir, who obligates for Garmi.

Rema: This is only for people. All agree that an animal is exempt.

Gra (2): The same applies to all such damage. According to Tosfos and the other Poskim (than the Rif) who distinguish Gerama from Garmi, this is only Gerama, for the person did not do it.

Question (Pnei Yehoshua 12b DH Piska): R. Shimon holds that Davar ha'Gorem l'Mamon (something that one does not own, but it saves him money) k'Mamon Dami (is considered like money). Why didn't we establish the Mishnah (about damage to Kodshim) to be like R. Shimon?

Answer #1 (Pnei Yehoshua): The Mishnah discusses damage of animals, and we do not obligate animals for causing losses. This is like Gerama. All agree that animals do not pay for Gerama.

Rebuttal (Ketzos ha'Choshen 8): R. Shimon holds that Davar ha'Gorem l'Mamon is like a bag full of coins. Surely, he obligates an animal that damages it! A Tosefta (4:1) says that if one has Acharayos for a Korban (he must bring another if it cannot be offered), he pays for its damage and is paid for damage to it. This is like R. Shimon.

Answer #2 (Ketzos ha'Choshen): We cannot say that the Mishnah is like R. Shimon, for it says that there is no Me'ilah. According to R. Shimon, there is Me'ilah for Kodshei Kodoshim, even if he has Acharayos for them.

Ketzos ha'Choshen (3 DH Mihu): The Rema exempts Garmi of one's money. This includes fire (that burned documents) when it is not his arrows, i.e. he should have fenced it but did not.

Kehilas Yakov (Bava Kama 35): Tosfos (Bava Kama 54a) asked why we don't say that "donkey" exempts a pit for damage to documents. The Nimukei Yosef could say that damage to documents is Gerama, and we never obligate for Gerama of one's property. However, the Ramban disagrees. At the start of Kuntres ha'Garmi, he says that we hold that Davar ha'Gorem l'Mamon Lav k'Mamon Dami, unlike R. Shimon. One who steals an ox sentenced to be stoned from the Shomer pays only principal, due to Garmi. R. Shimon, would obligate Kefel. If an animal tripped on a pit and fell outside the pit, even Shmuel exempts, for the floor of the pit did not damage it. Similarly, the pit did not physically damage the money lost through damage to the documents. The Me'iri says that his exemption applies only to a pit that one does not own. This is why the Ramban obligates for an ox that burned documents, even though it did not physically damage the money lost. However, since it did not did not damage directly, only through its Ko'ach, it should pay only half, like Tzeroros (pebbles that it kicked up that damaged)! It seems that the Rambam holds like Tosfos (17b), that we do not apply Tzeroros whenever the damage occurs immediately.