The black cat in folklore has been thought to shape shift into humans to spy and bring information and ingredients (such as rosemary) to their witches to use in spells.Therefore the cats are considered "bad luck" or a "bad omen" (and as a result are the least adopted kittens in the US!).
However, the award-winning astronomer Stephen James O'Meara debunks some of these myths in his book Are You Afraid Yet?: The Science Behind Scary Stuff. He claims that black cats may actually be good luck (as quoted in his interview on NPR's "Here & Now"):
"[Researchers have found that black cats] have a specific gene which helps them to fight diseases so they [live] longer. In fact, humans have the same gene within our own bodies and it may actually help us lead to antidotes."
Good! I knew I always found black cats intriguing for a reason. :)
Next week as Halloween approaches, I'll throw in some more Halloween mystery explanations. Enjoy!