Fascinated by a demonstration she saw as an undergraduate, of a pitchblende rock that seems to generate enough energy to take small photographs, Marie decides to make the rock's energy the subject of her doctoral study. The measurements she takes don't seem to add up, and she decides there must be a third radioactive element in the rock in addition to the two she knows are in it. In the midst of discussing this, she discloses offhandedly to Pierre's family that she is pregnant.