Edison tested it once it was built. He spoke into the mouth of the machine. He said, "Mary had a little lamb." The machine played back his ______. How could Edison build a sound machine if he was deaf? He had a trick. He ______ his ear up to the machine to feel it vibrate. Edison could have had an operation so he could ______ again, but he chose not to. He said that being deaf helped him. He said it let him think ______. Outside noises did not distract him at work. That was another part of his genius.