TB Khullin 121 Dead cows walking

When a Jew correctly ritually slaughters the animal immediately is considered dead even though it is still convulsing. According to Torah law, one may remove a limb to eat it without violating the law consuming a limb from a living animal, עבר מן החי. Nevertheless, rabbinic law demands that the animal stops convulsing before eating it.

When a non-Jew slaughters an animal, the animal is not considered dead until it stops convulsing. Consequently if the non-Jew removed a limb to eat while the animal was still convulsing, he has violated one of the laws given to Noah after the flood (עבר מן החי). Both Jew and non-Jew are forbidden to separate and eat a limb from a living animal.

Daf TB Khullin 121 discusses cases where the animal is considered both dead and alive according to Rabbi Yokhanan.

Case #1 a Jew which will be slaughtering a nonkosher animal:

 Rav Oshaya teaches (Tosefta, Oholot 2:1): In the case of a Jew who slaughtered a non-kosher animal for the consumption of a gentile, if he slaughtered it by cutting two simanim or the majority of two simanim, and the animal is still twitching, the animal imparts impurity of food (even though neither the Jew nor Gentile may eat the meat, it is still considered food because it was slaughtered in the kosher manner, i.e. dead according to halakha as described above-gg); but so long as it is twitching it does not impart the impurity of animal carcasses (but it is also considered not dead for the Gentile since is still convulsing-gg).

"A limb that separates from this twitching animal is considered like a limb that separates from a living animal, and as such it imparts the impurity of a carcass. And flesh that separates from this twitching animal is considered like flesh that separates from a living animal, and as such it does not impart impurity. And it is prohibited for the descendants of Noah to consume the flesh that separates from this twitching animal, and this prohibition applies even after its soul departs. This ruling of Rav Oshaya is in accordance with the opinion of Rabbi Yoḥanan.”

Case #2 a Gentile slaughtering a kosher animal:

“And similarly, in the case of a gentile who slaughtered a kosher animal for the consumption of a Jew, and the animal is still twitching, the animal imparts the impurity of food because it is considered to be food (even though it you may never eat it-gg), but so long as it is twitching it does not impart the impurity of an animal carcass.

“A limb that separates from this twitching animal is considered like a limb that separates from a living animal, and as such it imparts the impurity of a carcass. And flesh that separates from this twitching animal is considered like flesh that separates from a living animal, and as such it does not impart the impurity of food. And it is prohibited for the descendants of Noah to consume the flesh that separates from this twitching animal, and this prohibition applies even after its soul departs.” (Sefaria.org translation)

In both cases the animals considered both dead and therefore susceptible to the impurity of food, but still alive to prohibit flesh for the descendants of Noah. In other words, a dead cow walking.