Acting in Unison Stirs Up Aggression:

Military leaders have long known that marching in unison makes for a tight-knit platoon. Past research by psychologist Scott Wiltermuth of the University of Southern California Marshall School of Business suggests that this cooperation emerges when the group members’ emotions are aligned. Now he finds such synchrony can also encourage aggression, according to a study published in January in the Journal of Experimental Social Psychology.