If you'd asked me as a kid to make a sound like a fire truck, I'd have gladly shouted at the top of my voice "neeeew naaaaw, neeeew naaaaw, neeeew naaaaw," until someone yelled at me to stop. But then ...

RIO DE JANEIRO — Sound begins blasting ear drums and rattling bones even before the speakers — hauled by big rigs creeping their way through Brazil’s thronging Carnival crowds — draw near. The ...