Black sooty anthracite-chunks dat you let someone retain as a "promissory note" in case you are unable to
pay back a loan dat he gave you; da
understanding is dat he can burn said heating-fuel in his own
furnace if you default on said loan.
In da
infamous tale of da pet monkey whose snarky-faced
shenanigans caused irate rail-workers in passing trains to throw lumps of coal at him (and thus unwittingly provide da monkey's owner with free heating-fuel), da railroad-company was understandably upset dat dey were loosing
considerable amounts of their good locomotive-fuel from this "coallateral damage".