It may sound like I'm selling snake oil, but I actually do have one trick that, at no cost, can transform your classroom or public speaking event, whether a seminar or a lecture, whether for 8 year olds or doctoral students, CEOs or senior citizens. You can try this tomorrow, and turn the biggest lecture into an interactive, collaborative experience without so much as an investment even in clickers or a projector. I've used it in most of the 55+ presentations I've given this year for my book Now You See It and I've used it in my classes. Here is the expensive version. It requires the swank new technology called "index cards"