In 1990 a former prostitute named Fatou Sarre was tried in Alsace for the murder of her mother-in-law. Why, the prosecutor wanted to know, had Fatou, after bludgeoning Odile Gayean to death with a hammer, proceeded to gouge out her eyeballs? Fatou’s reply was simple but surprising: she had been afraid that the dead woman’s retinas would preserve an image of her in the act of murder. The curious thing – okay, one of the curious things – was that the origin of this belief wasn’t traced to Fatou’s childhood in Senegal, but to a Bollywood film she had happened to see, which itself had borrowed the notion from nineteenth- and early twentieth-century European fiction (by, among others, Jules Verne).

These novelists had been inspired in their turn by the work of distinguished scientists, serious truth-seekers, most notably Professor Wilhelm Kühne of the University of Heidelberg, who devoted years of his life to exploring whether ‘optograms’ might prove useful in crime investigations. Police hunting for Jack the Ripper actually took