This may be meant either, 1. Of a wicked heart showing itself in burning lips, furious, passionate, outrageous words, burning in malice, and persecuting those to whom, or of whom, they are spoken; ill words and ill-will agree as well together as a potsherd and the dross of silver, which, now that the pot is broken and the dross separated from the silver, are fit to be thrown together to the dunghill.
2. Or of a wicked heart disguising itself with burning lips, burning with the professions of love and friendship, and even persecuting a man with flatteries; this is like a potsherd covered with the scum or dross of silver, with which one that is weak may be imposed upon, as if it were of some value, but a wise man is soon aware of the cheat.
This sense agrees with the following verses.