  Fast scramblers process information in characteristic times scaling
logarithmically with the entropy, a behavior which has been conjectured for
black hole horizons. In this note we use the AdS/CFT fold to argue that
causality bounds on information flow only depend on the properties of a single
thermal cell, and admit a geometrical interpretation in terms of the optical
depth, i.e. the thickness of the Rindler region in the so-called optical
metric. The spatial sections of the optical metric are well approximated by
constant-curvature hyperboloids. We use this fact to propose an effective
kinetic model of scrambling which can be assimilated to a compact hyperbolic
billiard, furnishing a classic example of hard chaos. It is suggested that
classical chaos at large N is a crucial ingredient in reconciling the notion of
fast scrambling with the required saturation of causality.
