`` then a kind of ratchet aerates a dose and mixes it with a third substance that 's instantly permeated through a gel via a small incendiary- '' mr tate points to the end of the stick `` -and fired out here , vaporizing yet somehow holding cohesion until it hits its target , at which point- '' `` at which point it 's a burning acid corrosive enough to take your arm off , '' the mayor finishes .