Carter investigates what makes Slipknot tick in 2015 as they tour behind 2014's .5 The Gray Chapter - their first album following the death of founding member Paul Gray and the departure of drummer Joey Jordison.

Root explains the band's history has brought them closer together as a unit. He says: "I don't think any of us are really friends now, I think we're really brothers now. We don't see each other all the time, we don't call each other up, we don't go to each other's birthday parties, but we'd probably kill for each other still. We definitely would kill for each other still."

Gray's absence - and presence - are felt at the same time by percussionist Shawn Crahan, who gets emotional during a backstage tour as he opens the late bassist's wardrobe drawer.