"We knew the mice would sing different songs alone versus singing socially, but we didn't really understand the rules," says Arkarup Banerjee, another NYU neuroscientist and study author. So for their first experiment, they housed two mice that didn't know each other in a cage where they could hear but not see one another. By studying their musical conversations, Banerjee learned the rules: the mice are polite, and their songs are different when singing alone than with a partner. "They don't overlap their songs, and to do that, they have to be very cognizant of when the other mouse is stopping or starting a song," he says. When one mouse would stop, the other would reply within a split second—but unlike most humans, it would never interrupt