On a hot August evening in Central Park, Animal Collective played as the sky grew darker, the temperature dropped and the wind picked up, shaking leaves down from the trees onto the audience, until it carried the smell of rain, and then that rain itself, drizzling on a crowd whose mounting energy was rising by the minute. Everyone knew something was about to break, and the band seemed to love it, feeding off of that storm as they launched into their final song, “The Purple Bottle,” and the sky began to pour.