The hoodoo "Black Cat" spell is notorious. It was one of the most commonly reported hoodoo rituals I found described in historic reports when researching my book Conjurin' Ole Time (now republished as Conjuration) and even now, when few are still willing to deliberately harm animals in their magical workings, conjure products claiming to be Black Cat Bones and Black Cat Oil remain popular (even if most of these products no longer contain cats and serve as mere symbols of the tradition.)
The original purpose of the black cat bone was to render the user invisible. Over time it acquired a reputation for being able to produce other feats such as making the user immune to witchcraft, returning lost lovers and bringing tireless success in games. The ritual is said to have become known through certain versions of the St. Cyprian grimoire. Though named for an ancient saint, Owen Davies indicates that this grimoire only appeared in the 19th century.
However, it seems the Cyprian grimoire might be working from some much older ideas. I recently acquired the Hygromanteia, and in this book -- which dates at least to the middle ages if not earlier -- is the following spell for invisibility.
Take the head of a male cat. It must be a black one. Slaughter it in the name of the Father, and of the Son, and of the Holy Spirit, amen. When you slaughter it nobody else must be present. Do it at night. Put a broad bean in its mouth, two in its ears and two in its nostrils. Bring red earth and a new flowerpot and plant it there. Water it with human blood, or with the blood of a slaughtered beast. It must be watered by a virgin child -- the child must be nine or ten years old -- for forty days. Find a way so that the child will not forget this task. At the end of forty days, the broad beans are perfect. Then, bring a mirror. If you see your reflection, throw away the particular seeds. If you do not see your reflection, hold the seed in your left hand and go wherever you wish. It is glorious.
It is worth pointing out that the beans are an element of the original St. Cyprian spell, too. It's interesting that this version doesn't utilize the most off-putting aspect of the hoodoo version -- that is, boiling the cat alive. Hygromanteia says only to slaughter the cat, which can presumably done in more swift or more painless ways. In this version it's also not the cat's bone which is empowered, but the beans that were in the cat's presence. The beans of the Cyprian version are there but seem as if they're more of a 'spice' added to the cat-broth and are not of significant importance. Most of the hoodoo reports didn't even mention using beans.
Just another of the ways our folk magic traditions trace back to historical grimoires and ceremonial magic.