Related to yesterday's thing. There's also a great bit in the Mark Watson interview where he talks about the 40 minute lull you often get in one hour stand-up shows. He once, apparently, specifically addressed this by giving an audience member a stopwatch and asking them to chant LULL! LULL! LULL! at 40 minutes. That is genius. Thinking about the rhythm of attention is important and not something people normally do when they're writing a presentation. They tend to assume everyone's going to be focused for as long as they're going to talk. They're not. You have to design some peaks and troughs, assume there'll be some bits where they're not listening as hard.