  We adopt an operatorial method, based on creation, annihilation and number
operators, to describe one or two populations mutually interacting and moving
in a two--dimensional region. In particular, we discuss how the two
populations, contained in a certain two-dimensional region with a non--trivial
topology, react when some alarm occurs. We consider the cases of both low and
high densities of the populations, and discuss what is changing as the strength
of the interaction increases. We also analyze what happens when the region has
either a single exit or two ways out.
