 The varying gravitational influences of Pluto and Charon as they orbit their barycenter causes the chaotic tumbling of Pluto's small moons, including Kerberos.At the time of the "New Horizons" flyby, the rotational period of Kerberos was about 5.33 days and its rotational axis was tilted about 96 degrees to its orbit.The high axial tilt of Kerberos meant that it was rotating sideways relative to its orbit around the Pluto-Charon barycenter.