  Gravitation could modulate the interstellar scintillation of pulsars in a way
that is analogous to refractive interstellar scintillation (RISS). While RISS
occurs when a large ionized cloud crosses the pulsar line-of-sight,
gravitational interstellar scintillation (GISS) occurs when a compact
gravitational deflector lies very near to that line-of-sight. However, GISS
differs from RISS in at least two important respects: It has a very distinctive
and highly predictible time signature, and it is non-dispersive. We find two
very different astronomical contexts where GISS could cause observable
diffraction-pattern distortions: Highly inclined binary pulsars, and the kind
of compact interstellar clouds suspected of causing extreme scattering events.
