Even the dog's closest relative, the wolf, beat its cousin when food was placed on the opposite side of a fence, as shown in a 1982 study by Harry and Martha Frank of the University of Michigan.
People who took their place opposite him one by one, clutching a scrap of paper bearing the address of an overseas relative or else the business card of some European traveller, unwittingly exchanged in a moment of good humour for a lifetime of another person's hopes.