The presence of flowing blood in flesh causes the flesh to putrefy.
It is therefore necessary to purify the flesh of the animal from the impure flowing blood, by extracting maximum blood.
In Islamic Jurisprudence, Zabah is to cut the neck in order to severe the two jugular veins, the gullet and windpipe. It will suffice if any three of the four blood pipes are severed. The spinal cord should not be severed as it maintains connection between the brain and the body which enables convulsion after slaughtering. Convulsion squeezes out the remaining blood in the body.
The Islamic procedure of Zabah enables maximum extraction of blood, within a close circuit. The purpose of extracting maximum blood has been explained. The purpose of rapid extraction of blood is to avoid blood clots. Both aspects, removing flowing blood as well as avoiding blood clots are equally important to health. To explain this further, I seek refuge in the verse of the Quran (Maaida verse 3 and 4):
Forbidden unto you (for food) are carrion and blood and swine -flesh. And that which hath been dedicated unto any other than Allah, and the dead through beating, and the strangled, and the dead through falling from a height, and that which hath been killed by (the goring of ) horns and the devoured of wild beasts, saving that which ye make lawful (by the death-stroke), and that which have been immolated unto idols. And (forbidden is it) that ye swear by the divining arrows. This is an abomination. This day are those who disbelieve in despair of (ever harming) your religion; so fear them not, fear ME! This day have I perfected your religion for you and completed My favour unto you, and have chosen for you as religion AL-ISLAM. Whoso is forced by hunger, not by will, to sin; (for him) lo! Allah is forgiving merciful.
They ask thee (O Muhammad) what is made lawful for them. Say (all) good things are made lawful for you. And those beasts and birds of prey which ye have trained as hounds are trained, ye reach them that which Allah taught you ; so eat of that which they catch for you and mention Allahs name upon it, and observe your duty to Allah. Lo! Allah is swift to take account.