Rosalía and Billie Eilish have been two of the most exciting and inventive forces in pop music in recent years, so the idea of them coming together in one song is tempting. The conversation about a duet has been spreading for more than a year; in April, Rosalía told Zane Lowe that she was just waiting for Eilish’s vocal tracks. Apparently, Eilish finally sent them because the song was over, and now it’s out.