When I took an economics class in college, the professor came in the 1st day and without saying a word, started writing on the white board at the front. As soon as he filled it, he erased and started again. This happened 3-4 times and when he erased it the last time, he introduced himself and said nothing about what he had written and never mentioned it again...UNTIL
When he handed out the final exams, he said: "For those of you that took notes of what I wrote on the board on day 1, this exam will be easy as I wrote the questions and answers to this final exam."
Needless to say, very few, if any students had written that down, or if they did, remembered it at all.