"Ah, food!" Oscar licked his chops, and started to descend, but hesitated and looked doubtfully over his shoulder up the twisted, rock-ribbed ravine. "Boss," he said hesitatingly, "I think you ought to know and I was going to tell you when you got so free with that rock, but there's another of you blood-thirsty humans prospecting up this ravine, and he's got a gun, and when you started shouting for me, he quit prospecting and grabbed that gun, and started looking." "The devil!" Andy ejaculated. "Why didn't you tell me?" "I have. Duck, Boss...." Oscar flattened himself out of sight. * * * * * Andy needed no further urging. He squeezed his lithe six-feet down behind a boulder just as a heat beam hissed over his head. It hit the bluff behind him and he watched the dust boil out as the pulsing radio-frequency beam turned to heat. The gun worked that way. A thin radio-frequency special beam was projected and it continued on its way until it struck something, when it turned to heat. It didn't work worth a darn on Jupiter. The planet's soupy atmosphere turned the ray to heat within a dozen feet of the muzzle, but in space, or in the extremely thin atmosphere of Jupiter's moon, it was bad business. Andy cautiously stuck his head around the boulder. "Hey," he yelled, "cut out the shooting. What are you trying to do? This ain't the Fourth of July." "Get out of here," a shrill voice came floating down to him. "This is a free country and I'll stay here as long as I damn well please." In answer a heat ray singed the top of the rock he was hiding behind. "Blast 'im, Boss. He almost got you," he heard Oscar whisper. "I'll make him hard to catch," he answered, pulling his stumpy blaster from the holster at his back, and testing the spring to see if it was wound up to maximum capacity. The blaster was spring actuated, and hurled an explosive pellet about the size of a buckshot, which was really a tiny atomic bomb. Where that pellet hit, there was big trouble immediately, but the pellets in rare instances had been known to explode in the gun, in which case the person who had hold of the gun was never heard of again, so that blasters were not a favored weapon. Andy had picked this one up at a bargain from a technician whose nerves had gone bad from space strain and who no longer had enough guts to shoot it. Blasters were not used on Jupiter or Saturn. Too much atmosphere and gravity for even the most powerful spring to hurl the pellet far enough for the shooter to be safe. Andy poked one eye around the top of the boulder and squinted for a target. He was in the edge of the glow zone. Off yonder, 216,000 miles away, the mighty rim of Jupiter was visible. The sun was on the other side of Io, but reflected light from the planet supplied illumination much better than the best terrestrial moonlight.