  Gravitational lensing near a black hole is strong enough that light rays can
circle the event horizon multiple times. Photons emitted in multiple directions
at a single event, perhaps because of localized, impulsive heating of accreting
plasma, take multiple paths to a distant observer. In the Kerr geometry, each
path is associated with a distinct light travel time and a distinct arrival
location in the image plane, producing black hole glimmer. This sequence of
arrival times and locations uniquely encodes the mass and spin of the black
hole and can be understood in terms of properties of bound photon orbits. We
provide a geometrically motivated treatment of Kerr glimmer and evaluate it
numerically for simple hotspot models to show that glimmer can be measured in a
finite-resolution observation. We discuss potential measurement methods and
implications for tests of the Kerr hypothesis.
