"Yes, sir. I saw it." His voice sounded hoarse, muffled, and whispery coming through the damaged speaker. "Do you see what sudden damage can do to speaking apparatus?" "I must test," McGuire said, an almost hesitant note in his new voice. He spent fifteen seconds or so saying a series of nonsense syllables that are used as a test for a robot's speaking apparatus. They contain every sound used in English. When that was over, he said: "The damage inflicted has radically changed the basic patterns of the voice. If an equivalent amount of damage was done to Mr. Oak's vocal apparatus, then the voice which has been speaking must belong to Mr. Oak." "You saw the damage being done in each case," I said quickly. "You also see that it is the source of the voice that becomes important when the pattern has changed." "Yes, Mr. Oak. I see that." I breathed a deep, heartfelt sigh of relief. Felder looked at me in a sort of numb awe. "How did you figure that out?" "It came to me in a flash, but the clues were all over the place. McGuire didn't stay on the course I gave him; he couldn't, if he wanted to avoid meteors. And then, too you said that he ought to have more sensory apparatus, so that he could judge facts. The facts that come into his brain from his own sensory apparatus _have_ to be utilized in his memory banks. He didn't have to know all the steps in reasoning that would lead from one voice pattern to another if it could be demonstrated as a _fact_--as an axiom, if you like. "If _you_ tell him that he must change course, he isn't obliged to pay any attention; but if he spots a meteor, he has to accept that as a fact, and he changes course to allow for it. In a sense, then, the meteor is capable of giving McGuire orders, and you aren't." Felder didn't look any too happy; no one likes to have a point in his own field explained to him by a layman. But he couldn't argue with me. "There's a great deal more to be done before McGuire can be put into practical service," he said heavily. "We may as well head back to Ceres." "I don't think so," I said. "McGuire's in good enough shape to let us make the big splash on Earth that Ravenhurst wants to make. He'll need it if Viking is to have enough financial leeway to go on with this project." "What about ... what about Brentwood?" Vivian Devereaux asked. "We can get rid of him at Phobos just as easily as we can at Ceres. If there's any explaining of any kind to do, we can lay the blame on him. He won't be in any position to deny it." She nodded, understanding exactly what I meant. There were still plenty of bugs to be worked out of McGuire, but now I could see our way clear to getting both Thurston and Baedecker off our backs for a while. At that point, Brentwood stuck his head in the door. "What's going on?" he asked in his soft voice.