I think that there is also some connection between these linesand the belief in the power of "black cats" and other black living beings/objects in hoodoo/voodoo. "One of the most powerful animals to use in Voodoo was the cat, particularly, a black cat".http://www.neworleansghosts.com/voodoo.htm

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Here's a link to an interesting page that debunks the commonly held (American) superstitions about black cats being bad luck:

http://www.kinrossfolds.com/cattery/superstition.html

Here are some excerpts from that page:

"All cats, including black ones, were held in high esteem among the ancient Egyptians and protected by law from injury and death. So strong was cat idolatry that a pet's death was mourned by the entire family; and both rich and poor embalmed the bodies of their cats in exquisite fashion, wrapping them in fine linen and placing them in mummy cases made of precious materials such as bronze and even wood - a scarcity in timber-poor Egypt. ...

Dread of cats, especially black cats, first arose in Europe in the Middle Ages, particularly in England. The cat's characteristic independence, willfulness, and stealth, coupled with its sudden overpopulation in major cities, contributed to its fall from grace. Alley cats were often fed by poor, lonely old ladies, and when witch hysteria struck Europe, and many of these homeless women were accused of practicing black magic, their cat companions (especially black ones) were deemed guilty of witchery by association...

Many people believe that a black cat brings good fortune and also, that anyone who finds the one perfect, pure white hair in an all-black cat and plucks it out without being scratched, will find great wealth and good luck in love...

Whenever the cat of the house is black,
The lasses of lovers will have no lack." ~ English Proverb

Black cats aren't bad luck everywhere. In the English Midlands, a black cat as a wedding present is thought to bring good luck to the bride"...