I had a friend that was a system administrator. One of his favorite "puzzle questions" was: what just happened when you see this line in your terminal? .o:

I had a friend that was a system administrator. One of his favorite "puzzle questions" was: what just happened when you see this line in your terminal? .o: file not found (This was back when most people wrote C, compiled to .o files, then linked to a final executable.) The answer was you had typed: rm * .o While meaning to type: rm *.o Oops.