Warfare may have helped. When you see often enough some injuries and how people recover (or not) from them, some may see patterns and intuit recovery mechanism:

- Injuries to the lungs aren't always fatal but patients tend to have lasting breathing problems.

- Liver injuries... hmmm, make your eyes turn yellowish, and it seems like those who come from the region where they drink hot water with some plant inside tend to fare better than those who don't, and if you survive, eyes return to normal and you can make a full recovery.