By their fifth album, Led Zeppelin started evolving out of biting blues songs from black musicians like Muddy Waters, Memphis Minnie and Howlin’ Wolf, and into emo epics like “The Rain Song.” Four years after their debut, fans were accustomed to Robert Plant’s rock-god wail, Jimmy Page’s alternative-to-Clapton guitar histrionics, and John Bonham’s almighty stomp tearing through dark, electrified blues numbers. So here they flipped genres: funk parody (“The Crunge”), psychedelia (“No Quarter”), a reggae and doo-wop mashup (“D’Yer Mak’er”). The song decidedly didn’t remain the same.