Since I don't know what topics you already have, I hesitate making too many suggestions. But I would check the links below for some ideas. Good luck!
I would say when John Thorton tells buck to jump off the cliff and buck does it until Thorton catches him in mid air. Or you could do the time Francois was trying to put sol-lecks as lead but buck wouldn't move; those were some of my favorite pars of the book.