R. Zeira/ Rav Yehudah citing Shmuel: If one person had a cow and another had a donkey and they exchanged - if the donkey owner had taken the cow and the cow owner came to take the donkey and found it have broken limbs, the donkey owner must bring proof that the donkey was unblemished at the time that he took the cow.

Whoever does not reason like this statement does not understand the laws of damages at all.

R. Zeira: I personally do not reason like it so (perhaps) I do not understand damages at all. (R. Zeira reasons that we always follow the person who is in possession of the item; therefore, since the donkey owner is in possession of the cow and the cow owner wishes to take it from him, the cow owner must bring proof.)

Mishnah in Maseches Kesuvos: If a woman became betrothed and was later discovered to have blemishes; if they were discovered while she was still in her father's house etc. (If they existed before she was betrothed, the Kidushin can be invalidated; if they came after she was betrothed, the Kidushin is valid. If it is unknown when the blemishes came, the location that she is when the blemishes are discovered defines the outcome. Similarly, the ruling in the case of the donkey depends on the location of the dead donkey - therefore, since the dead donkey was found in the possession of the donkey owner, he must prove that it was healthy at the time of the exchange; otherwise, the cow owner is assumed to be correct.)

Rav Huna, R. Pinchas and R. Chizkiyah went to R. Yosi to question Shmuel (in (a)). They asked R. Yosi using the above Mishnah. He answered, "We can use the latter part of the Mishnah - If they found the blemishes after she had entered the domain of the husband, the husband must bring proof rather than the father. If so, it is the 'owner' who must bring proof. Here also, it should be the owner that must bring proof.''

Question (Rav Yehudah citing Shmuel): If one had a cow and one had a donkey and they exchanged; if the donkey owner took the cow, he acquires it. Is the donkey acquired?

Answer: R. Ba said that it is acquired. R. Yasa said that it is not acquired. (R. Yasa's opinion seems to contradict the Mishnah that says that it is acquired simultaneously).

R. Mana: There are some things here to which R. Yosi (i.e. Yasa) would agree - If a person said to him friend, "I wish to sell my cow'' and the friend asked him the price and he replied that it would cost 8 dinars

The buyer went and stood next to the money changer's table (and told the money changer to pay the seller the 8 dinars from his 'account'). The next morning, the seller stood next to the money changer's table and the buyer asked why he was there (since he did not owe him the money yet). The seller told him that he wanted to get the money that the buyer had promised him.

The buyer commented to the seller that he must wish to buy something with the money. The seller said that he wished to buy a donkey. So the buyer said, "Your donkey is with me'' (i.e. I will pay you for the cow with my donkey). When one took the animal, the other did not acquire the other animal and vice-versa (i.e. it is not actually a Kinyan Chalipin as the donkey is being used to pay for the cow rather than as an exchange).