A time-traveller and his student.. A college professor at a small college had just invented time-travel. He knew he couldn't trust just anyone with this secret, so he chose to tell only his best student; an african-american student named Mark. When the professor told him, Mark was shocked! ""So what do you plan to do with you time-machine?"" Mark asked. ""I'm going to kill Hitler when he was a child"" The professor responded. Mark was both appalled and intrigued, so he asked the professor if he could tag along. The professor thought that was a splendid idea, so he booted up the time-machine and waited for Mark to join him. A few seconds later they had arrived in a room with a person lying in wait to take the shot. He seemed unwilling to do so, for some reason. The professor walked up to the man and whispered uplifting words in his ear. Mark could hear him take the shot. Suddenly he realised that this wasn't Austria in the late 1800s. This was in Dallas, early 1960. The person he had who'd been shot wasn't Hitler, it was JFK. Mark broke down and cried, and when he looked up the professor and his time-machine was gone. On that day, the professor had left a black Mark in history.