Here's what happened to me. One slow Sunday afternoon, a man comes out of the restroom with a pearl necklace in his hand. "Found it on the bathroom floor" he says. He followed with "Geez, looks nice-I wonder who lost it?" Just then, the gas station's phone rings and a man asked if anyone found a pearl necklace that he had purchased as a gift for his wife. He offers a $200 reward for the necklace's return. I tell him that a customer found it. "OK" he says, "I'll be there in 30 minutes." I give him the ARCO address and he gives me his phone number. The man who found the necklace hears all this but tells me he is running late for a job interview and cannot wait for the other man to arrive.

Huum, what to do? The man with the necklace said "Why don't I give you the necklace and we split the reward?" The greed-o-meter goes off in my head, suppressing all rational thought. "Yeah, you give me the necklace to hold and I'll give you $100" I suggest. He agrees. Since high school kids working at gas stations don't have $100, I take money out of the cash drawer to complete the transaction.

You can guess the rest. The man with the lost necklace doesn't come and never answers my many calls. After about an hour, I call the police. The "pearl" necklace was a two dollar fake and the number I was calling went to a pay phone nearby. I had to fess up to my boss and pay back the money with my next paycheck.

Why did this con work? Let's do some . While the primary motivator from my perspective was greed, the pigeon drop cleverly engages our system. If you've been reading The Moral Molecule, you will remember oxytocin from earlier posts on robot brides, couchsurfing, and why we touch each other. Social interactions engage a powerful brain circuit that releases the neurochemical oxytocin when we are trusted and induces a desire to reciprocate the trust we have been shown--even with strangers.

The key to a con is not that you trust the conman, but that he shows he trusts you. Conmen ply their trade by appearing fragile or needing help, by seeming vulnerable. Because of oxytocin and its effect on other parts of the brain, we feel good when we help others--this is the basis for to family and friends and with strangers. "I need your help" is a potent stimulus for action.

Let's break down the oxytocin hooks that caused me to get conned. The first hook was the desire to help the man get this nice gift to his undoubtedly sweet wife. He needed my help. The second was the man who wanted to give the necklace back but who was late for his interview. If only I could help him get that job. My oxytocin system was in high-gear, urging me to reciprocate the trust I had been shown and help these people. Only then does greed kick in. Hey, I can help both men, make a wife happy, and walk away with $100-what a deal! Yes, suspend all suspicion and give up the cash. Cons often work better when a confederate poses as an innocent bystander who "just wants to help." We are social creatures after all, and we often do what others think we should do.

My laboratory studies of college students have shown that two percent of them are "unconditional nonreciprocators." That's a mouthful! This means that when they are trusted they don't return money to person who trusted them (these experiments are described in my post on neuroeconomics). What do we really call these people in my lab? Bastards. Yup, not folks that you would want to have a cup of coffee with. These people are deceptive, don't stay in relationships long, and enjoy taking advantage of others. Psychologically, they resemble sociopaths. Bastards are dangerous because they have learned how to simulate trustworthiness. My research has demonstrated that they have highly dysregulated oxytocin systems.

Oxytocin's effects are modulated by our large prefrontal cortex that houses the "executive" regions of the brain. Oxytocin is all emotion, while the prefrontal cortex is deliberative. I hope that by knowing that your oxytocin system can easily be turned on, you will be less vulnerable to people who might want to take advantage of you. But, don't be too vigilant: two percent of bastards isn't so bad. And, oxytocin causes us to empathize with others, the key to building social relationships. Russian playwright Anton Chekov said "You must trust and believe in people or life becomes impossible." I'd say that's about right-just watch for the occasional con.

Watch Skeptics Society founder Michael Shermer run the classic pigeon drop on the street in Westwood, CA.