But it was his eyes and not his ears that enabled him to fathom the secret of the Saturnians' greatest power: their ability to make themselves invisible. Whenever one of the monsters wished to vanish from sight, he merely dusted himself with a pale-blue powder from a purple-veined container. Evidently the powder--acting somewhat like a catalyzing agent--had the effect of causing the rays of light to pass completely through any object, thereby rendering it invisible. But did it make things invisible also to Saturnian eyes? The answer was in the affirmative: a Saturnian dusted with Amvol-Amvol could not be seen by any of his fellows, nor could the webs and cables, when concealed beneath this substance, be observed by their makers. This was, however, of little importance to Red-Hood and his followers; for they relied upon sight much less than did human beings. They were guided largely by what they called the Communication Sense: certain vibrations in the air, set up by their tails, were recorded by a bulging organ just under the left ear of each of the creatures; and thus they were able to learn of their whereabouts and doings of their kindred even when they could not be seen. So, at least, Gates concluded after long and careful observation. And his scheme for escape was built upon this knowledge. * * * * * But for a long while the plan did not take definite shape. And meanwhile he came to realize more keenly than ever how dangerous it would be to provoke his masters needlessly. For they had surpassingly quick and violent tempers; their rage was, literally, like a tornado. Many a time Gates, lying helpless in paralysis on a web in the Planetoid, was the terrified witness to one of their disputes. He was seldom able to decide just what the quarrel was about, the first that he ever knew of it was when a blast like a siren ripped at his eardrums. Then other siren blasts would follow; then spouts of smoke would leap through the air, and the acridness of sulphur would torment his nostrils; then, if he were in a favored position, he would see the adversaries facing one another, their tails lashing the atmosphere in long loops and spirals, their octopus arms threshing and writhing, while the screeching and bellowing would rise to a crescendo as of battling fiends, and the eyes of the competitors would blaze with fiery red flashes. There was one fight, in particular, which Gates would never forget. As usual, he had at first no idea of the cause; but the tumult this time was more diabolical than ever before. Paralyzed, he hung on a web several hundred feet above the floor of the Planetoid, in a grandstand position to view the affray. Among the lower meshes and cables, directly beneath him, Red-Hood stood amid steamy clouds of gas. And opposite him was an almost equally huge Saturnian, whose distinguishing features, as Gates saw it, was the clay-yellow coloration of his long tentacle-like claws.