If you Haul Somebody Over The Coals you give them a severe tongue-lashing, and perhaps find out the truth of something. In the 1400s, heresy was seen as a crime against the Church with a punishment of death. However, few ever confessed to adopting their own religious opinions, so it was often almost impossible to prove. The State came up with method of deciding on guilt. Any person accused of heresy would be tied up and dragged over a burning bed of charcoal. If they died then it was accepted that the person was a heretic and deserved it. However, if they lived they were believed innocent and freed, as it was thought that God had protected them. Not the most watertight system of justice.