Bikkurim, Chapter Two, Mishnah Ten
Here we learn in what ways a koy is similar to a domesticated beast.
And how is [the koy] similar to a behemah (a domesticated beast)?
1) Its fat (helev) is prohibited like the fat of a behemah, but one [who eats it] is not liable for karet.
2) It may not be bought with the money from second tithe to be eaten in Jerusalem.
3) It is subject to [the priests share of] the shoulder, the two cheeks and the maw.
a) Rabbi Eliezer exempts it because the burden of proof is upon the one who extracts from his neighbor.
Section one: Leviticus 7:23-25 prohibits eating the helev, a type of fat, from a domesticated animal (other types of fat are permittedotherwise how would we get shmaltz?). Since a koy might actually be classified as a behemah, one cannot eat its helev. However, since it is not definite that a koy is a behemah, one who does eat the helev of a koy is not liable for the punishment of karet (I just used four Hebrew terms in one sentenceI hope they were all clear).
Section two: Second tithe is redeemed outside of Jerusalem, the money is brought to Jerusalem and there it is used to buy food or drink. If one wishes to buy meat he can buy a domesticated beast such as a sheep to use as a sacrifice or he can buy a hayyah to just eat. He cant buy a koy to eat, because it might be a behemah and one can buy a behemah only to use it as a sacrifice. He also cant buy a koy to use as a sacrifice because it is not fit for sacrifice as it might be a hayyah, which are never used for sacrifices.
Section three: When one slaughters a domesticated animal as hullin (non-sacrificial), he has to give a priest the shoulder, the two cheeks and the maw. According to the first opinion, since a koy might be a behemah, when one slaughters a koy, he must give these to the priest. Rabbi Eliezer, disagrees and invokes the well-known principle that the burden of proof is upon the claimant. The priest would have to prove that a koy is a behemah in order to get these parts from an Israelite. Since he cant, the Israelite need not give them to him.