America’s Got Talent on June 14 when she performed a flawless cover of Canadian metal outfit Spiritbox’s song ‘Holy Roller’.The performance – which can be seen in its entirety below – sees the young British vocalist named Harper nail the opening verse and chorus of the track, leaving judges Simon Cowell, Sofia Vergara and Heidi Klum astonished.Following the performance, Cowell commented: “Have you ever seen a film called The Exorcist? Actually, kidding aside, that was brilliant. I mean, brilliant.