1) a burning or live coal

 A proverbial expression signifying to call up, by favours you confer
 on your enemy, the memory in him of the wrong he has done you (which
 shall pain him as if live coals were heaped on his head), that he may
 the more readily repent. The Arabians call things that cause very
 acute mental pain "burning coals of the heart" and "fire of the liver".