It had been still when the Saint first set eyes on it, but now it moved. It did not spread aimlessly over the floor; it was creeping along purposefully, as though imbued with life. The Saint, afterwards, described it as like a great, ghostly, luminous worm travelling sideways. Stretched out in a long line that reached from side to side of the greenhouse, it humped itself forward in little whirling rushes, and the living power within it seemed to burn more and more fiercely, until the cloud was framed in a faint halo of luminance from the whirl of eye-searing violet at its core.
It had seemed to be creeping at first, but then the Saint saw that that impression had been deceptive. The creeping of the cloud was now the speed of a man running, and it was plain that it could have only one objective. The goat at the end of the trough was cringing against the farthest wall, frozen with terror, staring wild-eyed at the cloud that rolled towards it with the relentlessness of an inrushing tide.
The Saint flashed a lightning glance back at the staging, and divined, without comprehending, why the cloud moved so decisively. The white-haired man was holding in one hand a thing of shining metal rather like a small electric radiator, which he trained on the cloud, moving it from side to side. From this thing seemed to come the propulsive force which drove the cloud along as a controlled wind might have done.
Then the Saint looked back at the cloud; and at that instant the foremost fringe of it touched the petrified goat.
There was no sound that the Saint could hear from outside. But at once the imprisoned power within the cloud seemed to boil up into a terrible effervescence of fire; and where there had been a goat was nothing but the shape of a goat starkly outlined in shuddering orange-hued flame. For an instant, only the fraction of a second, it lasted, that vision of a dazzling glare in the shape of a goat; and then, as if the power that had produced it was spent, the shape became black. It stood of itself for a second; then it toppled slowly and fell upon the concrete. A little black dust hung in the air, and a little wreath of bluish smoke drifted up towards the roof. The violet cloud uncoiled slothfully, and smeared fluffily over the floor in a widening pool of mist.