There is a saying in EOD (Explosive Ordnance Disposal) school that “the rules of the publications were written in blood”. This comes from the British bomb disposal units from World War II, who through sacrifice, trial, and error, paved the way for modern EOD. The current publications span decades, and are an expansive library of ordnance that technicians can refer to when identifying and rendering them inert.
As the Germans were bombing London during the blitz, hundreds of bombs did not detonate on impact. In some cases, they were designed to do so. Depending on the location of the bomb, they could not simply be blown up with additional explosives because it would damage infrastructure. Some bombs were buried in back yards, some stuck in the walls of buildings, and in many other areas. The bomb disposal units had no experience or manuals to assist them with dismantling these bombs. As a result, it was literally done by trial and error in the early stages of the effort.
A British bomb technician, always an officer, would shout his procedures to an enlisted man who was at a safe distance.