By 1991 Metallica had spent a decade building a reputation on speed and complexity. Then they slowed down, cut the song lengths in half, and released the heaviest thing most people had ever heard on commercial radio.

Enter Sandman opens with a riff that needs no introduction and a lyric about a child being told to say his prayers. It should not work on a mainstream chart. It went on to sell the album somewhere north of thirty million copies.

The sleeve is almost entirely black, a coiled snake barely visible in the corner. Thirty years later the band still opens or closes shows with it, and the crowd still handles the first four bars without any help.