  We explore how one might detect the dynamical quantum Cheshire cat proposed
by Aharonov et al. We show that, in practice, we need to bias the initial state
by adding/subtracting a small probability amplitude (`field') of the orthogonal
state, which travels with the disembodied property, to make the effect
detectable (i.e. if our initial state is $|\uparrow_z\rangle$, we need to bias
this with some small amount $\delta$ of state $|\downarrow_z\rangle$). This
biasing, which can be done either directly or via weakly entangling the state
with a pointer, effectively provides a phase reference with which we can
measure the evolution of the state. The outcome can then be measured as a small
probability difference in detections in a mutually unbiased basis, proportional
to this biasing $\delta$. We show this is different from counterfactual
communication, which provably does not require any probe field to travel
between sender Bob and receiver Alice for communication. We further suggest an
optical polarisation experiment where these phenomena might be demonstrated in
a laboratory.
