The reference to witch cake comes from a passage by the Rev. Samuel Paris, who said a meddling neighbor directed Parris’s Indian slave to make it. The evidence shows that the witch cake was a mix of some type of flour, such as rye, mixed with urine from the afflicted. They don’t know for sure how the cake was supposed to work; supposedly it was fed to an animal rather than to humans. Strange behavior by the animal was considered evidence that the person who had provided the urine sample was indeed bewitched.
The practice of baking a witch cake was considered an act of witchcraft by anyone who was religiously inclined; doing so was condemned as going to the devil to discover the devil.
Urine was common in efforts to in counter witchcraft. Some people also believed in boiling bent pins in urine.