  The question: "Where was a quantum particle between pre- and postselection
measurements?" is analyzed in view of a recent proposal that it was in the
overlap of the forward and backward evolving wave functions. It is argued that
this proposal corresponds not only to the criterion of where the particle
leaves a weak trace, but also where the local interactions can affect the
probability of postselection and where finding the particle in a strong
nondemolition measurement is possible. The concept of a "secondary presence" of
a pre- and postselected particle where local interactions affect the weak trace
in the overlap region is introduced.
