  When angular objects in lensing are considered as linear objects, interesting
phenomena start happening. Tachyonic caustics are one example. We review that
the intrinsic variables of the lens equation are angular variables. We argue
that the "fast glance effect" of a caustic curve that is far away from lenses
does not share the physical bearing of the well-known (apparent) superluminal
motion. There is no dbout that it would be a useful exercise to study the null
geodesics in the metric of, say, a rapidly rotating black hole binary.
Lienard-Wiechert potentials ($A_\mu$) satisfy Maxwell's equations in Minkowski
space. Authors' claim that swapping eQ and GM makes the time component ($A_0$)
of the Lienard-Wiechert potentials into "the gravitational analog" that governs
the behavior of the null geodesics near a relativistic binary system seems to
be unfounded.
