The other night, I was on a train, sitting across from two women who were sharing a single set of headphones—communal listening for those worried about disturbing the people around them. A man of their age and interested in, if not one, both, inquired after what was filling their ears. They giggled girlishly. "We discovered a new song this weekend," one said, "and we're sort of obsessed. It's called . . .... More >>>