  We investigate four key issues with using a nonzero weak value of the spatial
projection operator to infer the past path of an individual quantum particle.
First, we note that weak measurements disturb a system, so any approach relying
on such a perturbation to determine the location of a quantum particle
describes the state of a disturbed system, not that of a hypothetical
undisturbed system. Secondly, even assuming no disturbance, there is no reason
to associate the non-zero weak value of an operator containing the spatial
projection operator with the classical idea of `particle presence'. Thirdly,
weak values are only measurable over ensembles, and so to infer properties of
individual particles from values of them is problematic. Finally, weak value
approaches to the path of a particle do not provide information beyond standard
quantum mechanics (and the classical modes supporting the experiment). We know
of no experiment with testable consequences that demonstrates a connection
between particle presence and weak values.
