Once upon a time, they used to tell a story about a man who discovered his wife was a witch by this method—he had been coming across the field right at twilight when he saw a cat walking with the Devil. He sneaked up behind them to hear what matters they might be discussing and he realized he recognized the cat’s voice. It was his wife’s.
He rushed home, ransacked the house looking for her human skin, and, when he found it, he threw it in the fire. When she returned home and could not find her skin, she howled and screamed and then, when the sun arose, turned to ashes. Her soul immediately descended to Hell.
But there is another way the story goes, where the man returns home, drops his own skin, and runs off with his wife, both of them in the form of cats. They were never seen from again. I have not read this version, myself, but I hear that, in the old books, it has the title “Perplexing the Devil.”