“A WITCH! A witch! We have found a witch, may we burn her?” asks a marauding mob during a scene in “Monty Python and the Holy Grail”, a 1975 comedy film. “How do you know she is a witch?”, the king’s guard inquires. “She looks like one,” comes the reply. The accused witch’s defence is met with little sympathy. “They dressed me up like this. This isn’t my nose. It is a false one,” she cries in vain.

That parody is remarkably close to the truth. Between the 14th and 18th centuries about 80,000 people were tried for witchcraft in Europe. They were not all old, scraggly-looking women: 15% of Scottish witches were men, and their average age was 42. Their myriad alleged crimes were often trivial. A neighbourhood disagreement might escalate into accusations of sorcery if someone suffered a misfortune, such as a premature death in the family, after a quarrel. Around half of the accused were executed, usually by hanging or by being burnt at the stake.

European witch trials fell out of fashion around 1770. In recent decades, interest in them has focused mainly on re-enactments for hobbyists and tourists. But the subject has also bewitched a small group of scholars, who have combed through the surprisingly detailed data sets available on the practice and formulated theories to explain why they occurred when and where they did. While lacking the stakes of an actual witch trial, these researchers’ disagreements are still highly spirited by modern standards.

In 2004 Emily Oster, an economist now at Brown University, published a paper arguing that witch trials were linked to exogenous economic shocks. Accusations of witchcraft were most prevalent during the “Little Ice Age”, a period of particularly bitter winters in Europe beginning in 1590, which caused crops to fail and incomes to fall. Ms Oster speculated that medieval village-dwellers responsible for feeding poor older women in their communities may have cried witch in an effort to save scarce resources.

During a 164-year-long spell beginning in 1563, some 3,500 alleged witches were tried in Scotland, the second-highest rate per person in Europe. Based on Ms Oster’s theory, that time period should have been characterised by poor weather. However, a working paper by Cornelius Christian, an economics professor at Brock University in Canada, found that the Scottish climate was actually unusually balmy during that period, leading to bumper crop yields. That led him to the precise opposite conclusion from Ms Oster’s: people accused of witchcraft could only be persecuted with the co-operation of elites, he reasoned, who only had enough free time to chase down such prey when resources were plentiful.

There are more than two sides to the witch-trial debate. A recent paper by Peter Leeson of George Mason University and his former colleague Jacob Russ, argue that religious tensions, not the weather, put witch-hunters on the prowl. They gathered statistics from 43,000 European witch trials, primarily drawn from the mountainous areas near Lyon in France, Lucerne in Switzerland and Freiburg in modern-day Germany. Of these, three-fifths occurred during the period from 1560 to 1630 known as the “Great Hunt”, which was characterised by horrifying atrocities: in Würzburg, Bavaria, for instance, 400 people were executed on a single day.

The authors attribute this hysteria to the aftermath of the Protestant Reformation. Witch trials were most common, they found, in areas where Catholic and Protestant churches enjoyed comparable levels of support and were locked in a struggle for converts. Conversely, such trials were much rarer where one creed or the other predominated. Mr Leeson and Mr Russ noted a striking similarity to modern American presidential elections, in which the two major parties swarm closely contested “swing states” with ads and rallies while ignoring those where one has an insurmountable advantage. Perhaps witch trials served a similar function during the Great Hunt to the role of political campaigns today: instead of competing to show voters they offer protection from terrorists and criminals, 16th-century religions competed to show potential converts they offered protection from witches. The Florida—America’s biggest swing state—of early modern Europe appears to be Strasbourg in France: 30% of all witch trials on the continent occurred within 300 miles (500 km) of the city.

Of course, witch trials also led to the murder of tens of thousands of innocent victims. Modern politicians frequently court voters by warning of the perils posed by hidden enemies lurking in the public’s midst. They might be well-advised to consider whether the targets of the resulting policies are any guiltier than those accused of consorting with Satan just a few hundred years ago.