Jewish Law prohibits causing any pain to animals, the slaughtering has to be effected in such a way that unconsciousness is instantaneous and death occurs almost instantaneously.
Mark Twain once said, «Ignorance, intolerance, egotism, self - assertion, opaque perception, dense and pitiful chuckle headedness — and an almost pathetic unconsciousness of it all, that is what I was at 19 and 20.»