A man in a Batman costume stood silently on a Milan train, a few metres from a woman who appeared pregnant, and never once interacted with her or anyone else — yet his presence alone was followed by a jump in the share of passengers who offered her a seat from roughly one in three to two in three

He boarded through one door, stood roughly three metres away, spoke to nobody and touched nobody. A woman with a prosthetic belly stood in the carriage, every seat around her taken. Their field study in npj Mental Health Research found that on plain rides, someone offered a seat 37.66 per cent of the time. On rides with Batman aboard, that figure climbed to 67.21 per cent, an odds ratio of roughly 3.4. Of the 52 run by teams containing no author from the original paper, not a single one produced a significant effect in the expected direction, and the average effect sat at essentially zero.