Maaser Sheni, Chapter 3, Mishnah 11. The previous mishnah discussed a dispute concerning items purchased with maaser sheni money that became tamei: according to the Tanna Kamma, not only maaser sheni itself that became tamei may be redeemed, but even items purchased with maaser sheni money; Rabbi Yehudah disagreed and ruled that they are not redeemed but buried. Our mishnah discusses the status of a live animal purchased with maaser sheni money.
"Tzvi shelakcho b'chesef maaser umeis":
Someone bought a deer with maaser sheni money in order to eat it in Yerushalayim, and the deer died. The only option available to him is to redeem it. But such a redemption would only accomplish that the deer now serves as food for dogs, since it is fit for nothing else, and having died it was never rendered fit through shechitah. Here the Tannaim disagreed:
Tanna Kamma: "yikaver im oro" - the deer must be buried, and its hide is buried along with it.
Rabbi Shimon: "yipadeh" - it may be redeemed, and he feeds it to dogs. Rabbi Shimon holds that something that became sanctified can be redeemed, and once its sanctity has been removed it may be fed to a dog.
"Lekacho chai u'shchato v'nitma":
From here the mishnah moves to an aspect connected to the previous mishnah: someone bought the deer with maaser sheni money while it was still alive, then slaughtered it in order to eat it, and the meat of the deer became tamei. He cannot eat it, since it carries the sanctity of maaser sheni and it is tamei, and therefore the Tanna Kamma rules: "yipadeh" - it may be redeemed.
At first glance this is puzzling: in the previous mishnah Rabbi Yehudah disagreed and ruled that items purchased with maaser sheni money that became tamei are not redeemed. The commentators explain that here even Rabbi Yehudah agrees, for the following reason: since the deer was purchased with maaser sheni money while it was alive, it is not subject to the ordinary laws of maaser sheni. The passage in the Torah, which says that when a person is far from Yerushalayim he may redeem, together with the limitations placed on this halachah, all of this relates to maaser sheni itself and not to items purchased with maaser sheni money. This entire passage does not relate to a live animal at all, since a live animal can easily be brought to Yerushalayim on its own legs, and it does not present the problem of having to be carried and transported. For this reason it is not included in the passage, and therefore even Rabbi Yehudah agrees that it can be redeemed, even though it is an item purchased with maaser sheni money.
"Lekacho shachut v'nitma":
The mishnah continues: if he bought the deer after it had already been slaughtered, and it became tamei - "harei hu k'peiros". Its status is identical to that of maaser sheni produce, that is, to items purchased with maaser sheni money, which are the subject of the dispute in the previous mishnah between the Tanna Kamma, who said they are redeemed, and Rabbi Yehudah, who said they are not redeemed. The reason: although it originates from an animal, at the time it was purchased with maaser sheni money it was already slaughtered, and its status is that of ordinary produce.
In summary: our mishnah presented three cases of a deer purchased with maaser sheni money - a deer that died (a dispute between the Tanna Kamma and Rabbi Shimon whether it is buried with its hide or redeemed and fed to dogs); a deer purchased alive, slaughtered, and then rendered tamei (it is redeemed, and even Rabbi Yehudah agrees, since a live animal is not included in the passage); and a deer purchased already slaughtered that became tamei (its law is that of produce, and regarding it the Tanna Kamma and Rabbi Yehudah disagree as in the previous mishnah).