  On infinite homogeneous structures, two random walkers meet with certainty if
and only if the structure is recurrent, i.e., a single random walker returns to
its starting point with probability 1. However, on general inhomogeneous
structures this property does not hold and, although a single random walker
will certainly return to its starting point, two moving particles may never
meet. This striking property has been shown to hold, for instance, on infinite
combs. Due to the huge variety of natural phenomena which can be modeled in
terms of encounters between two (or more) particles diffusing in comb-like
structures, it is fundamental to investigate if and, if so, to what extent
similar effects may take place in finite structures. By means of numerical
simulations we evidence that, indeed, even on finite structures, the
topological inhomogeneity can qualitatively affect the two-particle problem. In
particular, the mean encounter time can be polynomially larger than the time
expected from the related one particle problem.
