Twenty-five years ago, at precisely 6.51pm on 16 December 1997, hundreds of children across Japan experienced seizures. In total, 685 – 310 boys and 375 girls – were taken by ambulance to hospital. Within two days, 12,000 children had reported symptoms of illness. The common factor in this sudden mass outbreak was an unlikely culprit: an episode of the Pokémon cartoon series.

The instalment in question, Dennō Senshi Porygon (Electric Soldier Porygon), was the 38th in the Pokémon anime’s first season – and initially, at least, it sparked a medical mystery. Twenty minutes into the cartoon, an explosion took place, illustrated by an animation technique known as paka paka, which broadcast alternating red and blue flashing lights at a rate of 12Hz for six seconds. Instantly, hundreds of children experienced photosensitive epileptic seizures – accounting for some, but far from all, of the hospitalisations.