A large part of traditional Paganisim and Witchcraft envolves using varrious parts from animals. Both in spellwork and in divination practice. In ancient Greece and Rome, there was a form of divination in which a freshly killed animal would be cut open, and there was a way in which the eternal organs, and intestiens would be read to predict future events.
As well many archaic spells call for such ingreidents such as the eyes of a newet, legs of a toad, heart of a bat, tails tounges, etc.. of a mutiltude of animals.
Of course this pratice is not widely and I would say rarely if ever still used today, and it is genreally frowned upon in this day and age, to harm other life for the sake of working magick.
But there are other ways in which the use of animals can still be implimented in magick today, as they still can offer a very potent componant to a spell of ritual. For by using the parts of an animal, you are inccoprerated the arritubutes and qualaties of that animal into your work.
Bones and antlers can sometimes be fond within the woods, and snake skin that had been sheded can be used, and well particuarly during the hot weather, it is not uncommon to find a repilte or amphibian that has been presevered and dried out by the sun which can be used and so forth.
Animal parts can also by bought, though you might want to make sure beforehand that the animal had died of natural causes.