Students enrolling on a new course on personal development were each given a small, colourful box. They were not told what it contained, but instructed to bring the box back to the first lecture the following day, and that under no circumstances should they open the box. This, they were told, was a strict rule which related to the matter of the course.
The students returned the next day and handed in their boxes. When the instructor opened them, she found that some were empty. There had been a small bird in each (no birds were harmed in this experiment). Obviously, as soon as it could, the bird had escaped when the overly-curious student had peeked.
Students’ reactions to the discovery that they’d broken the rule were mixed. A few became reflective, and one or two smiled. Others, by contrast, were quite upset, feeling that they had been duped. They said it was an unfair test, suddenly decided to become animal rights protesters, or even claimed the box had been empty when they opened it!