  The electron energy-loss function of graphite is studied for momentum
transfers q beyond the first Brillouin zone. We find that near Bragg
reflections the spectra can change drastically for very small variations in q.
The effect is investigated by means of first principle calculations in the
random phase approximation and confirmed by inelastic x-ray scattering
measurements of the dynamic structure factor S(q,\omega). We demonstrate that
this effect is governed by crystal local field effects and the stacking of
graphite. It is traced back to a strong coupling between excitations at small
and large momentum transfers.
