Imam al-Shafi'i (may Allah have mercy on him) says that Sayyiduna Umar (may Allah be pleased with him) forbade taking the knife down to the spinal cord when slaughtering, since in this way the soul departs without difficulty. Imam al-Shafi'i (may Allah have mercy on him) says: Nakh' is when a goat is slaughtered and then its neck is twisted from the place of slaughter so that its movement ends quickly; I dislike this. He says: Doing this does not make it unlawful; rather, it will be counted as slaughtered.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19134