There are a number of circumstances where it is clear that an animal (or a person) is dead, even though there still may be some spontaneous movement of the limbs of the animal. Thus, Rav Yehudah quotes Shmuel as saying that when someone’s neck is broken and the majority of the flesh in that area is torn, that person will already have the status of a dead body that ritually defiles the area where it is found. Although the Gemara points to a case where it appears that this status can be attained when the neck is broken even if the flesh remains intact – the story of Eli ha-Kohen who falls backwards and breaks his neck upon hearing that the Holy Ark was taken captive in a war with the Philistines (see IShmuel 4:18) – it explains that this was due to Eli’s old age and heaviness.
In the course of this discussion, the Gemara quotes a Mishnah in Masechet Oholot (1:6) that if an animal’s head is cut off, then there is immediate ritual defilement; it is viewed like the tail of a salamander that continues to twitch even after it is removed from the body of the salamander.
After the limb of a living creature is separated from the body, the nerves of that limb continue to operate in an uncontrolled manner for a short time due to the continued functioning of the neurotransmitters that still send out signals to the limb. Although the muscles continue to flex in response to these neurological signals, this is not necessarily an indication of life.
In contemporary discussions about establishing a working definition of “time of death” and the possibility that “brain death” – a cessation of all recorded brain-stem activity – may be viewed as halakhic death, the Mishnah in Masechet Oholot that discusses the ramifications of cutting off one’s head serves as a key source from the Talmud, opening the possibility ofharvesting organs for transplant purposes.