Mangle not only has 2 heads, she was the biter in the bite of '87! I proved this because Mangle is the only one who's jaw is wide enough to bite off your head. Back to the 2 heads thing. Mangle has 2 heads because she is ENNARD. Ennard's head looks just like the 2nd head on Mangle. Since Sister Location came before the second game, that means in the second game they took parts from Ennard. Still doesn't make sense? Well, Ennard's head was useful even if they didn't take it apart. So that means that Ennard's head was stuffed in one of either Mangle's arms or legs. So when the kids took her apart, the head probably just, sort of, popped out! So that is why Mangle has 2 heads! If you think i'm making a mistake in my theory, tell me in a comment!