Exclusive reactions induced at high momentum transfer in few body systems provide us with an original way to study the production and propagation of hadrons in cold nuclear matter. In very well defined parts of the phase space, the reaction amplitude develops a logarithmic singularity. It is on solid ground since it depends only on on-shell elementary amplitudes and on low momentum components of the nuclear wave function. This is the best window to study the propagation of exotic configurations of hadrons such as, for instance, the onset of color transparency. It may appear earlier in meson photo-production reactions, more particularly in the strange sector, than in more classical quasi elastic scattering of electrons. More generally, those reactions provide us with the best tool to determine the cross section of the scattering of various hadrons (strange particles, vector mesons) from the nucleon and to access the production of possible exotic states.
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