I've added a few lines about occultism and popular magic to "Animal Sacrifice and Blood Rituals in Traditional World Religions and Satanism" by Vexen Crabtree (2008):

Animal sacrifice has gone hand in hand with traditional and old religions6. The cradle of religion, animism, is rife with it. It is only the post-Roman Empire secular world that has fully rejected animal sacrifice. It remains in the holy books of the world's major traditional religions and is still practiced by many. It has in the past been a part of common, folk culture and folk religion; the resurgence of magic books, general occultism and popular belief in charms, luck, fate, etc, had led to a renewed interest in dusty old ritual magic. Will Emrish of the German Society for Protection against Superstition (DEGESA: Deutsche Gesellshaft vor Aberglauben, founded in 1954), who was also a former president of the German Animal Protection League, complained that "the Sixth and Seventh Books of Moses had led to the painful deaths of numerous cats, chickens, moles, and toads by followers of its magical cures".

I've added a few research studies to "Animal Sacrifice and Blood Rituals in Traditional World Religions and Satanism" by Vexen Crabtree (2008). The introduction to the text reads:

World religions such as Christianity, Islam and Judaism all embody a traditional and sometimes bizarre set of animal sacrifice rituals in their holy texts. These practices, despite being borderline barbaric and not in keeping with modern ideas of animal welfare, are still in use today by religious communities all over the world, including in the most modern countries. Although it might seem reasonable in the West to allow butchers to sell halal food, at the core of this familiar label is weird ritualistic behaviour that belongs in the dark ages. The ideals of pluralism have blinded us to the stark reality that some religious practices are simply unacceptable. Animal rights campaigners have joined forces with moral activists to try and curb religious ritual slaughter of animals. The general public associate blood rituals involving animals with Satanism, not realizing that they were all invented and are still practiced by mainstream religions - and that Satanism does not involve animal sacrifice. We compare scriptures below and look at some of the gory and shocking rituals that God directly asks people to do in the Jewish Scriptures / Old Testament. As modern governments continue to legislate against cruelty to animals, we will find that it is the world's mainstream religions' adherents who retreat to shady basements and hidden locations to perform secret rituals to kill animals, rather than Satanists or Pagans.

The studies include definitive proof that animals feel pain during religious ritual sacrifices when preparing Halal and Kosher food for Jews and Muslims. Stunning stops animals suffering completely, and it has been proven that stunning does not hinder blood draining.