Be that as it may, after some six years the results are in. But I do not know how to interpret the results. Perhaps you can help me. Here's how the experiment works:

On the first day of the semester, a student accomplice, posing as just another undergraduate, enters the lecture hall with her classmates and finds a seat somewhere in the middle. As students take their seats and wait for my arrival, my accomplice feigns finding a $50 bill under her seat (alternate semesters feature a lost iPhone). She holds it aloft and gives a self-congratulatory laugh. Shortly thereafter, I enter and begin class. Three or four minutes after that, a second accomplice (also posing as a student) knocks on the door. She explains that she's "pretty sure" that she dropped a large bill on her way out of this room fifteen minutes ago. Turning to the class, I ask students to look around their seats for money.

The first student, cool as a cucumber, makes a show of looking around her seat. Alas, no money. I let this play out for sixty--very tense, very awkward--seconds.

Now to fully appreciate the mood in the room at this point, you need to see the faces. (Of course, secretly recording and sharing these images with you troubles even the of a moral prankster.) Some faces reflect a kind of amused incredulity. Others reflect disgust. But one thing all the faces share is this: they are the faces of spectators. Not participants.

For in all the years that I have been running this experiment, only one student has ever exposed the thief. In all but a single case, I turn to the needy student and say: 'I'm sorry, we can't help you.'

To be sure, some students simply miss the business of finding the fifty. Others (I suppose?) would privately or anonymously tip me off later. The rest? It's none of their business.

Now I am not so naïve as to think that students would be lining up to snitch on one of their contemporaries. But what should I think? Is it that doing the right thing is especially difficult under these circumstances? Or is it that no student has a moral obligation to expose a thief in the first place? Am I expecting too much of them? Or not enough?