"Right," O'Brien broke in, "but you notice that the admiral said the antennae were the only difference noticeable to the eye. There's another, more important difference. The chemical make-up of the Zith body is such that water reacts violently on contact with it, producing what corresponds to severe burns, usually resulting in death. The admiral and I both noticed Sanderson's nervous habit down in the gun-bank a while ago. The pitcher incident a few minutes ago proved to us that Sanderson was not a Terran. You men noticed how he shook and paled when the water splashed near him." "Then this isn't Sanderson at all?" McDaniels asked, his dark eyes wide with wonder. "Our records indicate that a Lieutenant Vern Sanderson left Aldebaran II about three months ago to assist on the _Albion_ shake-down cruise. My guess is that the real Sanderson met with foul play somewhere along the way and this ... thing ... was substituted. The League knew that war was coming. They also knew that the Federation has lately installed the new Dyer gun and is in the process of installing the Bergesson Hyper-drive in its capital ships. This critter was probably one of many sent to get those secrets. With them, victory for the League would be assured." "But why kill him? Why didn't you take him prisoner and find out what he knew?" "For just one damned good reason," Harrigan answered. "These boys are telepathic over short distances--the antennae have something to do with that. If I hadn't taken him by complete surprise, he would have notified his pals, if any, on this ship. And, if there should happen to be a dozen or a hundred of these babies on board, we really would be in for it. O'Brien, arrange a watch on the mess hall. Have all hands who do not take water with their meals reported. You and chief Scott will have to call them in one at a time and give them the acid test." O'Brien went off to arrange the mess hall watch and Harrigan sat down, heaving a great sigh, behind his desk. "Well, gentlemen," he said, "you have seen the enemy. Or at least half the enemy." "Yes, sir," Rose responded, "but what about the Xantus, sir? I--we've never seen one of them." The admiral shuddered inwardly. "I hope you never do," he confessed. All the wretched memories of two galactic campaigns swept over him again. "A Xantu looks like nothing more nor less than a beer barrel on skids, with a cauliflower for a head. Eight independently focussing eyes, one for each of the tentacles that sprout from the middle of the chest. Get one of those monkeys behind a gun bank and you'll swear you have a platoon facing you." Harrigan lit a cigarette, forked smoke from his nostrils.