It could only mean that there was some mechanically symbiotic, emotion-sensitive electronic coating or skin surface, or series of tubes on the inner surface of the mask, which could simulate actual blood flow much like a network of tiny heat regulators. This network would be so responsive to the slightest change in body temperature that the mask would alter its color the instant the wearer experienced fright or grew uncontrollably angry. What made it seem logical and even likely was the fact that caloric changes do occur in just such a fashion in the human body with every shift from anger to grief or from pain to shock. There was nothing simple about the inner surface of the mask. It was a maze of complicated gadgetry concentrated in less than eight inches of space, perhaps thirty or forty separate mechanisms in all, some as tiny as the head of a pin, and others about one inch in width. When the wearer became unconscious, the mask seemingly lost its integrity. The gadgets either stopped functioning or ceased to function properly and the false face became a dissolving, hideous caricature; that bore little or no resemblance to the human countenance in repose, or even to the human countenance convulsed with sudden shock. How incredibly blind he had been in failing to suspect the existence of a mask when the guard's face had grown unnatural and ghastly in the cafeteria. He had taken it for granted that it was the man himself who had changed. Fortunately he was spared now from making the same mistake twice, and he took full advantage of the fact. He knelt again and began the by no means easy task of removing the uniform. He had to lift him up and turn him over twice and each time the man groaned and stirred a little. He seemed on the verge of coming to, but Corriston shut his mind to the possibility until the last of the man's garments had been tossed in a pile on the floor. He quickly took off his own uniform then, and carefully and methodically arrayed himself as a guard, taking care to leave the coat unbuttoned at the throat and even going so far as to draw on the heavy woolen socks and attach to his wrist the guard's metal identification disk. An audacious thought occurred to him, but he dismissed it at once. He could not attach the mask to his own face. It would have required the administrations of an expert, or, at the very least, someone familiar with the thing who knew exactly how it was supposed to be hooked into place. He had no way of knowing and he recoiled instinctively from the thought of hooks, however tiny, marring the skin on his face. No, he'd have to get along without the mask. No one on the lower levels knew him by sight, with the one ugly exception of a killer he'd never seen clearly enough to recognize in return. And in the guard's uniform he might even succeed in deceiving the killer if he moved quickly enough to give the man only a brief glimpse of him as he crossed the wide-view promenade. 10