Picture this. It's evening, getting dark. You're standing in the North Forest at Crystal Bridges Museum of American Art, and you hear something, the rhythms of 3,000 heartbeats. As you approach a certain grove of trees, you pick up on a subtle mix of whispering voices. Do you stop to add your own? When you get to the three enormous light robots, one of them begins to imitate your movements, and each one sets off swooping sounds.