  We use three dimensional simulations with coupled hydrodynamics and Monte
Carlo radiative transfer to show that shadows cast by the inner disc in broken
circumbinary discs move within a confined range of position angles on the outer
disc. Over time, shadows appear to rock back and forth in azimuth as the inner
disc precesses. The effect occurs because the inner disc precesses around a
vector that is not the angular momentum vector of the outer disc. We relate our
findings to recent observations of shadows in discs.
