el weon de gas

There are these trucks, carts too, that drive around the cerros of Valparaíso with canisters of gas, for use in kitchens, to heat the califont, etc. Estadounidenses, remember the ice cream man? He drives around playing music so everyone knows he is the neighborhood, and those within earshot run over to the truck. Well, this is the same idea, but with canisters of gas. They bang a wrench or something against the canisters, and so attract customers with their incessant rattling. I have heard the sound before but never understood why until one drove by at the mosaic pilars and I bothered to ask what the noise was for.