  To better understand the possible breakdown of locality in quantum
gravitational systems, we pursue the identity of precursors in the context of
AdS/CFT. Holography implies a breakdown of standard bulk locality which we
expect to occur only at extremely high energy. We consider precursors that
encode bulk information causally disconnected from the boundary and whose
measurement involves nonlocal bulk processes. We construct a toy model of
holography which encapsulates the expected properties of precursors and compare
it with previous such discussions. If these precursors can be identified in the
gauge theory, they are almost certainly Wilson loops, perhaps with decorations,
but the relevant information is encoded in the high-energy sector of the theory
and should not be observable by low energy measurements. This would be in
accord with the locality bound, which serves as a criterion for situations
where breakdown of bulk locality is expected.
