1.   After a year had passed, McCain and Brace were communicating with other prisoners in the camp, shuttling messages back and forth with the tap code.

2.   Messages were sent using a tap code taught to prisoners as they came in.

3.   On one video, two men explain the tap code devised for communication between prisoners in Vietnam, with each letter of the alphabet assigned a number of taps.

4.   Using a cup to the wall, McCain could hear the other prisoner and managed to give him the tap code.