Not all witch’s food is edible, nor is it all really “food.”  It was once a popular belief in Sweden that witches sent their cats out to steal food from neighbors, especially butter.  According to legend, these witches’ cats once ate so much butter that they vomited it up on their way home.  Thus the yellow bile that cats sometimes cough up is called “witch’s butter.”

— The Element Encyclopedia of Witchcraft by Judika Illes

A troll cat is gray and round like a ball of wool, and it rolls along the ground.  It sucks milk from the cows and sneaks into the houses to steal cream.  When the troll cat sucks itself too full, it slobbers all over, and the spilled cream turns to gray paw butter, which people also call troll cat vomit and troll cat butter.  One can see it on the ground in the morning after a foggy night; it covers planks and logs in the fields where the troll cat has run during the night.

— Scandinavian Folk Belief and Legend by Reimund Kvideland and Henning K. Sehmsdorf