  Electromagnetic and Lorentz-scalar form factors are calculated for a bound
system of two spin-less particles exchanging a zero-mass scalar particle.
Different approaches are considered including solutions of a Bethe-Salpeter
equation, a ``point form'' approach to relativistic quantum mechanics and a
non-relativistic one. The comparison of the Bethe-Salpeter results, which play
the role of an ``experiment'' here, with the ones obtained in ``point form'' in
single-particle approximation, evidences sizable discrepancies, pointing to
large contributions from two-body currents in the latter approach. These ones
are constructed using two constraints: ensuring current conservation and
reproducing the Born amplitude. The two-body currents so obtained are
qualitatively very different from standard ones. Quantitatively, they turn out
not to be sufficient to remedy all the shortcomings of the ``point form'' form
factors evidenced in impulse approximation.

High Energy Physics - Phenomenology;Nuclear Theory