The wisdom of the Islamic rules of slaughtering is to take the animal's life in the quickest and least painful way; the requirements of using a sharp instrument and of cutting the throat relate to this end. It is forbidden to rend the throat by using teeth or nails since this will cause pain to the animal and is likely to strangle it. The Prophet (peace be on him) recommended sharpening the knife and putting the animal at ease, saying, Allah has ordained kindness (or excellence) in everything. If killing is to be done, do it in the best manner, and when you slaughter, do it in the best manner by first sharpening the knife and putting the animal at ease. (Reported by Muslim on the authority of Shaddad bin Aus.)

In another hadith narrated by Ibn'Umar, the Prophet (peace be on him) said, "When one of you slaughters, let him complete it," (Reported by Ibn Majah.) meaning that one should sharpen his knife well and feed, water, and soothe the animal before killing it.

Ibn 'Abbas reported that once the Prophet (peace be on him) saw a man who was sharpening his knife after laying down a sheep to be slaughtered. The Prophet (peace be on him) rebuked him saying, "Do you intend to make it die two deaths? Why did you not sharpen your knife before laying it down?" (Reported by al-Hakim, who classified it as "sound" according to the standard of al Bukhari.)

Once 'Umar saw a man dragging a sheep by its leg to be slaughtered. He said, "Woe to you! Lead it to its death in a decent manner." (Reported by 'Abd ur-Razzaq.)

Thus the main intent here is to be kind to the unfortunate animal and spare it unnecessary suffering insofar as this is possible. The people o f jahiliyyah were fond of cutting off the humps of live camels and the fat tails of live sheep in order to eat them. In order to put a stop to this barbaric practice, the Prophet (peace be on him) forbade the eating of any part obtained in this fashion, saying, "Any part cut off a living animal is dead flesh," (Reported by Ahmad, Abu Daoud, al-Tirmidhi, and al-Hakim.)