Have arrived early in the morning to give an illustrated talk on my work. An enthusiastic crowd is gathering asking daft questions like Where do you plug in your camera ? (In the computer, I reply.) Gasp of admiration. They should be an easy audience. "I 'll just get the video tape and then we can begin," I say. I rummage through the contents of my suitcase - loads of weird things inside: bundles of electrical components, a small black book, and a plastic superman bound up in sellotape. But of course NO tape. I have nothing to show.