Really good ears

In the middle of the novel Rome's Revolution, Rei is coming up to speed as to how the Deucadons got to where they are, dwelling in caves deep beneath the planet. They explain that living underground presents a lot of problems. Things that normal people take for granted like fresh air, fresh water, waste disposal; all of these were something that they had to build. They became masters of conduit science, the science of getting things from Point A to Point B efficiently.

One of their crowning achievements was their invisibility cloaks. They used their mastery of conduits to build suits so that the Vuduri could not find them. They were distressed that Rei not only saw them, but came wandering into their camp. Here's how that little discussion went:

     “Yes,” answered Melloy. “When the Vuduri first came here, we approached them and without so much as a word, they slaughtered our people. They came huntin’ for us. We were well hidden but it was nawt from them but it became so. Only one or two times have they found us. Each time there was death. We wear these camouflage suits, which are designed to be invisible to the Vuduri eye.”
     To demonstrate, Steben stood up, pulled a hood over his head and ran his hands along his clothes. About halfway down, he literally disappeared from view.
     “Wow,” Rei said. “How does that work?”
     “The cloth contains light pipes, conduits, which bring images from the back to the front and vice versa,” replied the disembodied voice. “It conducts visible, infrared and ultraviolet as well. We do nawt even have a heat signature.”
     “Wow,” Rei said admiringly. “You guys have mastered invisibility. That is too sleek.”
     “Yes, we have,” answered Steben’s voice. “Which reminds me. I should nawt only be invisible to them. I should be invisible to ya too. There was naw way ya should have seen able to see me. Yet ya did. How is that?”
     Steben winked back into view.
     “Yes, and it was pitch black. So, Mr. Rei, how was it that ya saw Steben?” asked Melloy.
     “I didn’t see him,” Rei said. “I heard him.”
     “Steben is well-trained in the stealth arts. How did ya hear him?”
     “I have really good ears,” Rei said.
     “Ya must have,” said Melloy.

Well, what Rei did not exactly tell them was that he had sonar-vision which was a gift from OMCOM. It wasn't that he was keeping it secret but more that revealing it would just slow down the process of him getting back to the secret Ibbrassati enclave to the North.