Of course they almost all took a go at teaching duty, that was just part of the agreement. However, Ten simply ended up doing it more. You've a natural talent for it, they'd told him. You're so personable and animated!
Truth was, he'd drawn the short straw. Aaaah, well. Beat staring at Nexus time-currents until one's eyes crossed or spying on Fenric schmoozing all about the place and what is he up to with that, anyway?
At any rate, there he was, now. And to-day was review day.
"Hallo, everyone!" he said once everybody was seated. "To-day, we're going to have a bit of a review on causality." He writes the word on the whiteboard in big letters as is his wont. "Cause and effect. Post hoc ergo propter hoc, as the Romans called it--after this, thus, because of this--they hated it when people got it in their arguments, but it's often unavoidable in debate and even more so in physics."
People sometimes get whiplash during this Doctor's lectures, he moves about so much. "'Every major decision creates ripples'," he says, pacing about. "That much is obvious. Refer back to what some theorists call Temporal Nexus Points, Schroedinger Points, or Everett Nodes." Now he's sitting on the desk. "They theorise that every event causes time to branch, creating more timelines, and continues to do so, resulting in an infinite web of timelines, especially for the Multiple Universalists." Grin. Now he's at the whiteboard again, having drawn a line and now a branch with another and another off that and so forth. "Bit of an example. Now. In the Nexus, this doesn't apply, but in realities, it does. Every action affects time."
He turns to look back at the rest of the room for the inevitable first round of questions.