Grandfather told me. He taught in his youth in our political school. There is another stream for the lecture. With strict walks, so almost everything. Grandfather lectures, nobody listens, someone is sleeping, someone is whispering. They can be understood: 8 o'clock in the evening, most after work, tired. Grandfather turns out the lights in the audience and says: guys who want to sleep sleep, you can listen to the rest. And continue the lecture.) It is winter on the street, so there is darkness in the audience. The most interesting thing is that when he turned on the light, nobody was sleeping, everyone was sitting and listening carefully))