The rule of asham taluy appears in the Torah (Vayikra 5:17-19), and its rules are discussed in detail in the fourth perek(=chapter) of Massekhet Keritot that begins on today’s daf (page). The Torah does not specify what transgression would obligate this sacrifice to be brought; nevertheless, there is a long-standing Rabbinic tradition which teaches that an asham taluy was brought when a person accidentally performed an act that may have been forbidden by the Torah – one for which he would have been obligated to bring a korban hatat (a sin offering) had we known for sure that the act was prohibited.
The tanna’im differ as to the level of uncertainty that obligates a person in an asham taluy, but the conclusion is that the sacrifice is brought only in the case of hatikhah ahat mi-shtei hatikhot – “one piece out of two.” This means that an asham taluy is only brought when the question is whether an act which is forbidden was done. If, however, there is a question with regard to the act itself, i.e. we are not certain whether the act was forbidden at all, then an asham taluy would not be brought. The specific example given is a case where a person had two pieces of meat in front of him: one was permitted and one was forbidden; we are certain that he ate one piece, but we are unsure which piece it was. Another such case would be if we knew for certain that the piece was forbidden, but we are uncertain as to whether the person ate the minimum amount necessary to be obligated in a sin-offering. In these two cases, an asham taluy would be required. If, however, we are not sure whether the piece that was eaten was truly forbidden – it was a case of hatikhah ahat, “a single piece” – then an asham taluy would not be brought.
Rabbi Eliezer disagrees with this analysis and rules that someone who ate the helev of a koy is obligated to bring an asham taluy. Helev is the fat of an animal that is forbidden if the animal is domesticated, but permitted if the animal is a wild animal.
Identifying the koy is a difficult task. Even though it is mentioned many times in the Mishnah and Talmudic literature, that is not because it is a common animal, rather because its status between a wild and domesticated animal allows it to serve as a test case for many halakhot. The disagreement as to its identification began in the time of the Mishnah, when some of the Sages argued that it is the offspring of a deer or similar animal with a goat. Others claim that it is a unique type of animal – an Ayal ha-bar.
The Ayal ha-bar can be identified with the ovis musimon, which, according to many, is the forerunner of domesticated cattle. It is distinguished by its short hair and grey color, and it lives in mountainous regions, where it is a nimble climber – today mainly in uninhabited areas in Europe. It is likely that the clear similarities between a koy and a sheep, together with its being a wild animal, led to the Sages’ confusion about its classification.
Its name, “koy” and even the pronunciation of the name, are themselves the subject of disagreement.