  In very well defined part of the phase space, $K N$ and $\Lambda N$
rescattering depend on on-shell elementary matrix elements and on the low
momentum components of the deuteron wave function. This provides us with the
unique opportunity to study details in the scattering amplitudes that may have
escaped the analysis of reactions induced on a nucleon target by Kaon and
Hyperon beams at low energies. When folded with a typical experimental mass
resolution, a narrow state with a width of 1 MeV would contribute by no more
than 10% to the $KN$ mass spectrum. On the contrary, a cusp would be easily
detected near the $\Sigma$ production threshold in the $\Lambda N$ mass
spectrum.
