Bava Kamma

For if you assume that it has Scriptural authority, then as soon as he starts the act of slaughtering in the slightest degree would he not render the animal ritually forbidden for any use, so that what follows the beginning would amount to slaughtering an animal no more belonging to the owner? — R. Aha, the son of Raba, said to him: The liability might be just for that commencement in the slightest degree. R. Ashi, however, said to him: This is no refutation;  [since it says] 'and he slaughters it' we require the whole act of the slaughter, which is absent here. But what about the original difficulty?  — He, thereupon, said to him that R. Gamda stated thus in the name of Raba: When does he become liable? When for instance he cuts a part of the organs of the animal outside of the 'Azarah but completes the slaughter inside of the 'Azarah. MISHNAH. IF A THIEF [IS CONVICTED OF THE THEFT OF AN OX] ON THE EVIDENCE OF TWO WITNESSES, AND OF THE SLAUGHTER OR SALE OF IT ON THE EVIDENCE OF THE SAME TWO, AND THESE WITNESSES ARE SUBSEQUENTLY PROVED ZOMEMIM,  THEY MUST PAY [THE ACCUSED] IN FULL.  IF, HOWEVER, THE THEFT [HAS BEEN ESTABLISHED] BY THE EVIDENCE OF ONE PAIR OF WITNESSES, AND THE SLAUGHTER OR SALE BY THAT OF ANOTHER PAIR,  AND BOTH PAIRS ARE PROVED ZOMEMIM, THE FIRST PAIR MAKES [THE ACCUSED] DOUBLE PAYMENT  AND THE SECOND PAIR THREEFOLD PAYMENT.  WHERE [ONLY] THE SECOND PAIR WERE PROVED ZOMEMIM, THE THIEF MAKES DOUBLE PAYMENT,  WHEREAS THEY PAY [HIM] THREEFOLD.  SHOULD ONE OF THE SECOND PAIR OF WITNESSES BE PROVED ZOMEM, THE TESTIMONY OF THE SECOND PAIR BECOMES NULL AND VOID.  SHOULD ONE OF THE FIRST PAIR OF WITNESSES BE PROVED ZOMEM, THE WHOLE TESTIMONY [OF BOTH PAIRS] BECOMES NULL AND VOID, FOR IF THERE WAS NO THEFT THERE COULD BE NO [ILLEGAL] SLAUGHTER OR SALE. GEMARA. It has been stated:  If a witness has been proved a zomem, Abaye says that he becomes disqualified retrospectively [from the time when he gave his evidence in court],  whereas Raba says that he is disqualified only for the future [from the time when he is proved zomem]. Abaye makes the disqualification retrospective on the ground that the witness has been shown to have been wicked at the time when he gave evidence, and the Torah says: Do not accept the wicked as a witness.  Raba, on the other hand, holds that the disqualification begins only from the moment when his deceit is proved, because the whole procedure of proving witnesses zomemim is anomalous. For this is a case of two witnesses against two; why then accept the evidence of the one pair rather than that of the other? At least let it take effect only from the time when the anomalous procedure is employed. Some say that Raba really agrees with Abaye that the disqualification is retrospective, but rejects here this principle on practical grounds, because its adoption