Doc Enhanced Hearing

Doc popped the corridor lights off as a matter of safety. He feared no encounter in the dark. He had trained his ears by a system of scientific sound exercises which was a part of the two hours of intensive physical and mental drill Doc gave himself daily. So powerful and sensitive had his hearing become that he could detect sounds absolutely inaudible to other people. And ears were all important in a scrimmage in the dark.

- The Man of Bronze (1933) Chapter 4