It was a tape of human skin, cut from the silhouette of the dead man. That is to say, the cut had been begun at the right shoulder, and the knife—going carefully in a double slit so as to make a tape—had gone down the outside of the right arm, round the outer edge of each finger as if along the seams of a glove, and up on the inside of the arm to the arm-pit. Then it had gone down the side of the body, down the leg and up it to the crotch, and so on until it had completed the circuit of the corpse's outline, at the shoulder from which it had started. It made a long ribbon.
The way to use a Spancel was this. You had to find the man you loved while he was asleep. Then you had to throw it over his head without waking him, and tie it in a bow. If he woke while you were doing this, he would be dead within the year. If he did not wake until the operation was over, he would be bound to fall in love with you.
--Once and Future King, TH White