"This is so exciting for me," Gaga tells the band. "My friends are gonna hate me on Sunday." At one point during the rehearsal, Gaga locks into Metallica bassist Robert Trujillo's groove, allowing the singer to put her imprint on the Hardwired… to Self-Destruct track.
"Wow, a singer who appreciates bass," Hetfield says to Gaga, who responded, "I can't find my pitch without bass."
Despite the practice that went into the collaboration, the actual Grammy night performance was ultimately marred by technical difficulties.
"There was a slight technical snafu, but that's not really something you can do much about," Lars Ulrich told Rolling Stone. "You just learn to live with that side of it. It happened to Adele last year; I guess this year it was our turn."
"Mic Into Flame?," the band wrote in a note to fans. "Ok, our little Grammy … hiccup … wasn't that dramatic. But it still left all of us wondering, 'What if?' To answer that question and do justice to what we felt was an inspiring collaboration, we decided to share footage from earlier that day when all cylinders were firing just right."
Soon after the Grammys, Metallica and Lady Gaga posted an onstage rehearsal video of "Moth Into Flame" to show fans how the performance was supposed to go down.