Van Halen frontman David Lee Roth, King Solomon, medieval trials, life insurance policies and Nigerian e-mail scams don't appear to have much in common. But a classic Freakonomics podcast explains that they're all examples of "teaching a garden to weed itself", or using incentives to persuade certain people to separate themselves from others.
In medieval times, people accused of a crime were presented with two options: plead guilty or undergo a trial by ordeal. In the latter, priests would command the accused to grab hold of a scalding metal rod or pluck a rock out of a cauldron of boiling water, and pronounce them innocent if they weren't badly burned. That may seem like a barbaric and pointless exercise, but economics and law professor Peter Leeson argues that it rooted out criminals quite successfully.
At the time, most people believed in an omniscient God who knew whether they were guilty or innocent. Therefore, the guilty were reluctant to choose a trial by ordeal - they would be burned and convicted of the crime - while the innocent saw it as their best chance at absolution. Church records from 13th-century Hungary detail 208 cases of people consenting to grab a red-hot iron bar to prove their innocence; more than two-thirds of them were exonerated. Rather than divine intervention, Leeson believes the priests were aware that an innocent person's incentive was to assent to the ordeal. So they rigged the trials, perhaps by lowering the temperature.
The simple act of choosing a trial by ordeal revealed information about an individual's guilt or innocence. King Solomon famously solved a dispute between two mothers in a similar fashion. Both had recently given birth, but one had rolled over in her sleep and crushed her newborn. Now both women were claiming ownership of the remaining child, and came to the king to resolve the argument. In a moment of inspiration, the king called for his sword and threatened to slice the baby in half and split the parts. The pretender was happy with the solution; the real mother cried out and said she would rather give the child up than see it killed.
Rock star David Lee Roth elicited crucial information using a similar system. When Van Halen toured, it provided a detailed contract to every local promoter that listed technical specifications, food and drink requests and other information. As the band's shows featured huge, complex stage sets and cutting-edge audio and lighting systems, it was vital that the venue manager read the contract thoroughly to prevent any accidents. Roth claims he invented a clever trick to check the promoter's attention to detail: in the 'snacks' section of the contract, after potato chips, dips and pretzels, it said: "M&Ms (NO BROWN ONES)". Many put the request down to rock star extravagance, but if the band found brown M&Ms in the dressing room, it would conduct a serious line check.
On the podcast, Freakonomics authors Steven Levitt and Stephen Dubner also reveal that they lied in Superfreakonomics. In the book they recommended that terrorists buy life insurance from their bank, as many forego it as they have few family attachments and most policies don't cover suicide. The pair claim that not buying it would be a red flag. But it was actually a ruse intended to identify terrorists - at least those gullible enough to follow the advice. Most people don't buy life insurance from their banks, and most life insurance policies do cover suicide. Levitt's thinking was that only would-be terrorists would be incentivised to go to the bank and buy life insurance.
Similarly, police officers often withhold details of a crime in the hope that suspects volunteer them, outing themselves as the perpetrators. And Nigerian scammers purposefully send out blatantly fraudulent emails so they only receive responses from the most gullible people - those most likely to send money to a stranger halfway across the world.
*Former Guardian editor Alan Rusbridger recently mentioned King Solomon's dilemma in a Times Higher Education blog about University of Oxford admissions. When a candidate was asked for a better solution, he or she suggested the king offer a price high enough to deter the pretender.