Once William Thomson (Lord Calvin) had to cancel a lecture and wrote on the blackboard: "Professor Tomson will not meet his classes today ". The students decided to play a trick on the professor and erased the letter "c" in the word "classes". Next day, when Thomson saw the inscription, he did not become confused, and, having erased one more letter in the same word, left the classroom.
Есть две бесконечные вещи — Вселенная и человеческая глупость. Впрочем, насчёт Вселенной я не уверен.