Hot irons had to be held and later blisters were evidence of guilt and witchcraft. The methods of torture used by the Catholic Inquistion were so gruesome that people would confess to anything to stop the pain.

@ASTRALMAX True, what many people do not know, and a fact that the Catholics like to keep quiet, was that the inquisition was not set up to persecute "Misbelievers" such as Muslims and Jews, its original purpose was the extirpation of other Christian sects such as the Cathars, Anabaptists, Arianists, Donatists and other Gnostic churches.
Killing a single member of these false religions could purchase a Knight a plenary indulgence, that forgave not only all sins committed by the warrior, but also forgave any sin he might choose to do in the future and still guarantee his place in heaven without the purging fires of purgatory.