Well, I'm a mere student, but we did play a trick on our instructor. He went on vacation for a week, so his instructor was teaching our classes, and he took some form, 1 kata if I recall correctly, and changed 1 move in it, and told all the students to do that 1 move differently. Well, our instructor came back, and after watching someone's 1 kata, he corrected the student. Right away, everyone jumped in with, "No, you told us it was this". It lasted about three days before one of the kids cracked.