BUENOS AIRES: On a recent Sunday, a Buenos Aires plaza transformed into a makeshift wilderness for an unusual group of teenagers. Sofía, wearing a lifelike beagle mask, ran across the grass on all fours. Nearby, 15-year-old Aguara leapt through the air, clearing an obstacle course while imitating the precise movements of a Belgian breed dog. Others dressed as cats and foxes perched in the branches of trees, keeping their distance from curious onlookers. It was the latest gathering of “therians,” individuals who say they identify mentally, spiritually or psychologically with non-human animals.