Marty McFly: [on walkie-talkie to Doc] Doc! Biff's guys chased me into the gym and their gonna jump... me!
Doc: [on walkie talkie to Marty] Then get outta there!
Marty McFly: [on walkie-talkie] No, Doc. Not *me*, the *other* me, the one that's up on stage playing "Johnny B. Goode."!
Doc: [on walkie-talkie] Great Scott! Your other self will miss the lighening bolt, you won't get back to the future and we'll have a major paradox!