  The fluctuation-induced interaction between two rod-like, rigid inclusions in
a fluid vesicle is studied by means of canonical ensemble Monte Carlo
simulations. The vesicle membrane is represented by a triangulated network of
hard spheres. Five rigidly connected hard spheres form rod-like inclusions that
can leap between sites of the triangular network. Their effective interaction
potential is computed as a function of mutual distance and angle of the
inclusions. On account of the hard-core potential among these, the nature of
the potential is purely entropic. Special precaution is taken to reduce lattice
artifacts and the influence of finite-size effects due to the spherical
geometry. Our results show that the effective potential is attractive and
short-range compared with the rod length L. Its well depth is of the order of
\kappa/10, where \kappa is the bending modulus.
