The aforementioned wedding - of the New Scientist reporter Linda Geddes and her fiance - took place at a country house in Devon, south-west England, where Zak set up a temporary research station. He took blood samples, before and after the wedding vows, from the bride and groom, close family members, and various friends in attendance, then flew back his spoils - 156 test tubes, packed in dry ice - to his laboratory at Claremont University, in southern California. There, he discovered the results he had been expecting: the ceremony caused oxytocin to spike in the guests. And it did so in spookily subtle ways: the bride recorded the highest increase, followed by close family members, then less closely involved friends, "in direct proportion to the likely intensity of emotional engagement in the event". (Only the groom bucked the trend: testosterone interferes with oxytocin, and his testosterone was surging.) Mapping the wedding's oxytocin levels gave rise, in Zak's vivid phrase, to a human "solar system" with the bride as the sun, the hormone finely calibrated to the emotional warmth each guest felt. "It was amazing," Zak recalls. "Just this perfect sense of how oxytocin attunes to the environment."