Generally speaking, only healthy animals can be slaughtered for kosher food. Thus, a tereifa – an animal that has a terminal condition – cannot be used. Nevertheless, if an animal is merely a mesukenet – it is ill – and its owner wants to slaughter it so that he can benefit from its meat, the Mishna teaches that such sheḥita would be kosher, assuming that the animal shows a sign of vitality when killed. According to Rabban Shimon ben Gamliel this would require movement of the animal’s limbs; according to Rabbi Eliezer, it is enough if blood spurted out at the time of sheḥita.
Then said I, ‘Ah, Lord God, my soul has not become impure; and from my youth until now I have not eaten an unslaughtered carcass [neveila], or one torn of beasts [tereifa]; neither came there abhorred [piggul] flesh into my mouth.’
This statement was made after God commanded Yeḥezkel to eat disgusting things, and the prophet’s response was to object that he had always been careful to avoid anything that was not pure and untainted. The simple explanation is that Yeḥezkel was arguing that as a kohen he had to be even more careful than ordinary Jews regarding the food that he ate, as neveila and tereifa are not only unkosher, but ritually impure, as well. Nevertheless, the Sages of the Gemara understood that the prophet could not possibly have prided himself in simply keeping the straightforward halakha. They therefore interpreted the passage as follows:
‘My soul has not become impure,’ for I did not allow impure thoughts to enter my mind during the day so as to lead to impurity at night.
‘And from my youth until now have I not eaten of neveila or tereifa,’ for I have never eaten of the flesh of an animal concerning which it had been exclaimed: ‘Slaughter it! Slaughter it!’ [i.e., the flesh of a dying animal, which was slaughtered with haste before it died.] ‘And no piggul flesh came into my mouth,’ for I did not eat the flesh of an animal with regard to which there was uncertainty and a Sage pronounced to be permitted.
Thus we find that avoiding such meat is a stringency that Yeḥezkel kept, but that others are not obligated to keep.