"You see Fuz McGinnis and I have known each other always. We used to have a secret dot-and-dash code when we lived back home, used to tap each other messages." Hal seemed to forget for the moment that he was up before the "Benzine Board," was being washed out of flying forever perhaps. He warmed to his subject. "It just occurred to me that while we were up in the air, it might come in pretty handy sometime to send the other fellow a message. You might need to tell him something, or ask for help quick! The motor running is about all you can hear in the airplane. So it just came to me to take a try at making the motor do the talking, to cut it and race it in a sort of code."