In the experiment, when a spectator observed a relative or friend walk across hot coals, both the onlooker and performer's heart rates changed at the same time, though they didn't match each other beat for beat.

(See "Why Fire Walking Doesn't Burn: Science or Spirituality?")

Past studies have observed that sports fans' hearts race when their teams score, but no one had yet delved into the physical effects on both spectators and participants, according to study co-author Ivana Konvalinka, a Ph.D. student at the Center of Functionally Integrative Neuroscience at Denmark's Aarhus University.

The finding suggests social bonds between people may manifest themselves even more powerfully than thought, Konvalinka noted.

The results show that "we can find markers of emotional connectedness in