An ordinary activity is started, with no mention of first aid. Then the activity reaches a stage where one of the team members becomes injured. The team have to react as if the leader is not there and ensure the injured person gets first aid and help.
We ran this with an indoor climbing wall, allowing an Explorer to climb 3ft off the ground then appear to go unconscious. The Explorer was briefed beforehand and had agreed with the Leader how to react. It would work playing football or similar but this was a particularly successful ruse.
The injured person needs emergency help, to be safely moved to the floor to prevent trauma from the harness and the group need to work together to achieve this.
Once on the ground we agreed to move the injured person by stretcher downstairs. The leader assists the team to understand what needs to be done, but where there are Explorers who know what to do they are encouraged to lead the team.
A definite leader will arise from this situation and the team will either panic or work well together. This all leads to a good de-brief at the end.
As this works only for a finite group, Max 5, the others are encouraged to brush up and basic understanding like the acronyms DRABC and FAST. In particular the stroke Face, Arms, Speech, Time to Call 999 acronym is good for Explorers to learn and pass on this knowledge.