Pam Belluck in the NYT:

The results surprised them. The heart rates of relatives and friends of the fire-walkers followed an almost identical pattern to the fire-walkers’ rates, spiking and dropping almost in synchrony. The heart rates of visiting spectators did not. The relatives’ rates synchronized throughout the event, which lasted 30 minutes, with 28 fire-walkers each making five-second walks. So relatives or friends’ heart rates matched a fire-walker’s rate before, during and after his walk. Even people related to other fire-walkers showed similar patterns.

Experts not involved in the study said despite the small number of participants, the results were intriguing. They build on research showing heart rates of fans of team sports surge when their teams score, and on studies demonstrating that people rocking in rocking chairs or tapping their fingers eventually synchronize their movements.