Most likely the overwhelming stench of death, the dying, human bodily fluids, mud, gun powder, poison gas and smells you could not even imagine. I'm 72 years old and when I was a kid back in the early 1940s there was still a lot of vets from WW1. There were a few of those fellas who still suffered from the effects of war gasses. Mustard, phosgene and chlorine and they all had different effects on the body from respiratory dermal and neurological.