A woman in France in 1959 is waiting in her room, with all the doors locked from the inside, for her husband to come home. When he arrives, the house has burned to the ground and she's dead. How come?
The hot sun reflected from the woman's large mirror (which may have been imperfectly flat and therefore focused the sunlight) and heated the lingerie she was wearing to the burning point. She was absorbed in a book at the time and didn't notice the heat until her clothing was afire. Nobody could get to her to help because her doors were locked from the inside.