Great Regulars: When your knees become tired, when your

clothes wear out from rubbing, when you feel squeezed in the crowd at a public lecture--this is all, according to Rava, the work of demons. And there are magical ways of making demons show themselves. All you have to do is find a black female cat who is the firstborn daughter of a firstborn mother, burn her placenta to ashes, grind the ashes, and put some of them in your eye, and you will be able to see the demons. Be sure, however, to place the remainder of the ashes in a sealed iron tube, lest the demons steal it from you.

from Adam Kirsch: Tablet: The Talmud's Many Demons

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