Shechita is performed with a surgically sharp instrument (a chalaf), which must be perfectly smooth without the minutest notch or irregularity. The shochet constantly examines the instrument to ensure this standard is maintained. The frontal structures at the neck - including the trachea, esophagus, the carotid arteries and jugular veins - are severed in a rapid and uninterrupted action causing an instant drop in blood pressure in the brain. This results in the immediate and irreversible cessation of consciousness and sensibility to pain. Proponents of stunning seek to achieve the state of unconsciousness by additional intervention, but shechita humanely incorporates this loss of consciousness as an integral part of the procedure, which renders the animal insensible to pain, and brings exsanguination with a rapid action.
Exsanguination is the bleed-out of the carcass. This is especially important in Jewish law as Jews are forbidden to consume blood (Deuteronomy XII:23). Exsanguination is necessary in all methods of animal slaughter since blood deteriorates quickly and could putrefy the meat if it is retained in the animal. Shechita ensures maximum exsanguination.
There are five Halachic requirements that the shochet is obliged to ensure in the performance of shechita, (Shulchan Aruch, Yoreh De'ah 23):
a) There should be no interruption of the incision (shehiya);
b) There should be no pressing of the chalaf against the neck (derasa), this would exclude use of a guillotine;
c) The chalaf should not be covered by the hide of cattle, wool of sheep or feathers of birds (chalada), and therefore the chalaf has to be of adequate length;
d) The incision must be at the appropriate site to sever the major structures and vessels at the neck (hagrama);
e) There must be no tearing of the vessels before or during the shechita process (ikkur).
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