  In term of the volume-integrated Poynting vector, we present a quantum
field-theory investigation on the zitterbewegung (ZB) of photons, and show that
this ZB occurs only in the presence of virtual longitudinal and scalar photons.
To present a heuristic explanation for such ZB, by assuming that the space time
is sufficiently close to the flat Minkowski space, we show that the
gravitational interaction can result in the ZB of photons.
