  In the framework of a final state interaction model, we show that the
so-called radial flow, i.e. the almost linear increase of the inverse slope $T$
with the mass of the produced particle, is already contained in the initial
condition -- with a slope $<u_t^2>$ (the so-called strength of the average
radial transverse flow) which is larger than the measured one. While the
precise value of the slope depends on the details of the model, the above
result has a very general basis -- namely the increase with increasing $p_T$ of
the fixed $p_T$ suppression, in the low $p_T$ region.
