This episode opened with a flashback to the day Clara Oswalds parents met. Their chance meeting was occasioned by a leaf blowing in the wind at the exact right time that catches the father in the face and makes him stagger into the path of an oncoming car, only to be saved by the woman who would become Claras mother. Setting aside the slightly contrived nature of the meeting, we can recognize that the encounter reintroduces a theme that has recurred in Doctor Who throughout its run the questions of destiny, fate, and what determines them. From a storytelling perspective, the leaf is also a well-placed use of the Chekhovs Rifle device. In the end, it is not the Doctors thousand-year memory that staggers the Slumbering God, but a simple leaf with an infinity of possibilities contained within it.