By the time the four Gryffindors had reached the ground floor of Malfoy Manor, the place was as quiet as—well, a tomb. The foursome had been prepared for a pitched magical battle, from the moment they had entered Malfoy Manor, but no such battle had happened. When the foursome still had been on the fourth floor, all the Death Eaters on the fourth floor had suffocated; whilst the Death Eaters on lower floors had run down to the ground floor to escape the deadly lime-green gas—not knowing that chlorine gas, like shit, rolls downhill.