  A massive intruder in a homogeneously driven granular fluid, in dilute
configurations, performs a memory-less Brownian motion with drag and
temperature simply related to the average density and temperature of the fluid.
At volume fraction $\sim 10-50%$ the intruder's velocity correlates with the
local fluid velocity field: such situation is approximately described by a
system of coupled linear Langevin equations equivalent to a generalized
Brownian motion with memory. Here one may verify the breakdown of the
Fluctuation-Dissipation relation and the presence of a net entropy flux - from
the fluid to the intruder - whose fluctuations satisfy the Fluctuation
Relation.
