To be clear, I generally have a two to three hour discussion/lecture with my students before we get wet. We cover safety, signals, the physics of diving (trim, buoyancy & propulsion), tissue groups (safety stops), listening for your buddy and what to expect from the class. Even here, I aim to keep things fun and moving right along. Why not? There's no need to waste anyone's time: theirs or mine. In the water, I try to speak as little as possible. It's monkey see/monkey do. Why describe a complex task when I can show them? If a picture is worth a thousand words, then a demonstration is worth a bazillion.