  We study the behavior of two particles moving in a bistable potential,
colliding inelastically with each other and driven by a stochastic heat bath.
The system has the tendency to clusterize, placing the particles in the same
well at low drivings, and to fill all of the available space at high
temperatures. We show that the hopping over the potential barrier occurs
following the Arrhenius rate, where the heat bath temperature is replaced by
the granular temperature. Moreover, within the clusterized ``phase'' one
encounters two different scenarios: for moderate inelasticity, the jumps from
one well to the other involve one particle at a time, whereas for strong
inelasticity the two particles hop simultaneously.
