Keritot, Chapter Three, Mishnah One
Our mishnah talks about various types of cases where a person might or might not have eaten forbidden fat, a transgression that would cause him to bring a hatat for atonement.
1) If they said to him: you ate forbidden fat, he is liable to a hatat;
2) If one witness says: he ate, and another says: he did not eat, or if one woman says, he ate, and another says, he did not eat, he is liable to an asham talui.
3) If one witness says, he ate, and he himself says, I did not eat, he is exempt.
4) If two [witnesses] say, he ate, and he himself says, I did not eat:
a) Rabbi Meir says he is liable.
i) Rabbi Meir said: if two witnesses are capable of bringing upon him severe penalty of death, can they not impose the less severe punishment of a sacrifice?
ii) They replied: suppose he said, I did it intentionally, would he not be exempted?
Section one: This is the obvious case. If a person ate a piece of fat and doesnt know whether it was helev (forbidden fat) or shuman (permitted fat), then he must bring a hatat.
Section two: In this case, there is contradictory testimony with regard to whether the fat he ate was forbidden. Furthermore, there is either only one witness who testifies that he ate forbidden fat, or that witness is a woman, whose testimony does not fully count. Since there is no proper testimony, he does not bring a hatat. However, he does bring an asham talui, a suspended asham. As I explained in the introduction to Keritot, this is a sacrifice brought when it is not clear if a person transgressed.
Section two: In this case, there is no solid testimony that he ate forbidden fat, and he himself denies having done so. These two factors combine to exempt him from having to bring a sacrifice.
Section three: In this case, there is proper testimony against him, but he himself denies having eaten forbidden fat. Rabbi Meir argues that just as in a case of the death penalty, where two witnesses can make him liable, so too here, when it comes to bringing a sacrifice to atone for a sin, two people can make him liable, even if he denies having transgressed. The other rabbis argue against Rabbi Meir by noting that there is a difference between testimony for a capital crime, such as murder, and testimony with regard to liability for a sacrifice. In the case of the sacrifice, if the person admits to having eaten the forbidden fat, but claims to have done so intentionally, he is not obligated for a sacrifice, because sacrifices are brought only for accidental sins. Therefore, when he says, I didnt eat he is believed.