  The dynamics within active fluids, driven by internal activity of the
self-propelled particles, is a subject of intense study in non-equilibrium
physics. These systems have been explored using simulations, where the motion
of a passive tracer particle is followed. Similar studies have been carried out
for passive granular matter that is driven by shearing its boundaries. In both
types of systems the non-equilibrium motion have been quantified by defining a
set of "effective temperatures", using both the tracer particle kinetic energy
and the fluctuation-dissipation relation. We demonstrate that these effective
temperatures extracted from the many-body simulations fit analytical
expressions that are obtained for a single active particle inside a
visco-elastic fluid. This result provides testable predictions and suggests a
unified description for the dynamics inside active systems.
