Short version, the person working with the bomb would call out what they saw, then do what the partner said. The partner had a book and was out of the blast radius. They recorded it all, and if the bomb blew up would write down not to do THAT again!

Eventually they learned to somewhat reliably disarm the bombs by this type of trial and error. And then the other side would add better booby traps to stop them from succeeding.

Crazy.