Ten years after leaving Iraq, the hardwired lessons of war still manage to sneak up on me. The lingering effects of PTSD became clear to me in 2015. I was on a northbound train from New Delhi to the India-Pakistan border, when a chocolate vendor hopped on board our crowded 54-bunk sleeper car. The man across from me declined politely. Then he leaned toward me. I should never buy from the vendors, he said, because sometimes they inject drugs into the food.