Chullin 32 - Pause During Shechitah
If in doing the shechitah one properly severed the trachea, but tore the esophagus with a nicked knife, then Rabbi Yesheivav says that the animal becomes a nevelah - not slaughtered at all - and therefore carries ritual impurity. Rabbi Akiva says that the animal becomes a trefah: it is slaughtered, but considered to have an internal defect that would cause it to die within a year. Trefah cannot be eaten, but it does not carry ritual impurity.
Rabbi Yesheivav stated a rule: any animal that became unfit through slaughter becomes a nevelah, but if another incidental defect caused it to become unfit, it becomes trefah, and subsequently Rabbi Akiva agreed to it.
Art: Gerard Terborch - Woman Washing Hands
