One day, a professor entered the classroom and announced a surprise test. Hearing this, all students got anxious and started thinking about what would come up in the test. The professor distributed the question paper, with the front side facing down. After handing over the papers to all the students, he asked them to turn the page and start the test. To everyone's surprise, there were no questions on the test paper. There was just a black dot in the center of the page. Everyone was startled and looked at the professor in awe.