  The fractal velocity pattern in symmetric kink-antikink collisions in
$\phi^4$ theory is shown to emerge from a dynamical model with two effective
moduli, the kink-antikink separation and the internal shape mode amplitude. The
shape mode usefully approximates Lorentz contractions of the kink and antikink,
and the previously problematic null-vector in the shape mode amplitude at zero
separation is regularized.
