  We investigate a simple toy model of particle scattering in the flat
spacetime limit of an analogue-gravity model. The analogue-gravity medium is
treated as a scalar field of phonons that obeys the Klein-Gordon equation and
thus admits a Lorentz symmetry with respect to $c_\mathrm{s}$, the speed of
sound in the medium. The particle from which the phonons are scattered is
external to the system and does not obey the sonic Lorentz symmetry that the
phonon field obeys. In-universe observers who use the exchange of sound to
operationally measure distance and duration find that the external particle
appears to be a sonically Lorentz-violating particle. By performing a sonic
analogue to Compton scattering, in-universe observers can determine if they are
in motion with respect to their medium. If in-universe observers were then to
correctly postulate the dispersion relation of the external particle, their
velocity with respect to the medium could be found.
