At eleven on Monday, Dr. Ibrahim went alone to the lecture room in the Faculty of Medicine. There were about forty students waiting there for him. “I’m sorry,” he said, “I won’t be able to give my lecture today.” The students looked surprised. Dr. Ibrahim explained that he had an important sudden meeting. “However” he went on “Although I can’t be with you myself, my voice can! He gestured towards the cassette recorder on the table. “You see, I’ve recorded my lecture and you can listen to it while I go to the meeting. So, in a way, I’ll be in two places at once! One of the miracles of modern science! “Feeling rather pleased with himself Dr. Ibrahim switched on the cassette recorder and left. The meeting finished a little early. So, Dr. Ibrahim decided to go back to the lecture room. He stood a moment outside the door, listening to his voice. Then, very quietly, he opened the door. To his surprise, the room was empty. But then, as he looked around he saw a number of small cassette recorders, all listening to his lecture.