  The presence of strange sea quark pairs may have a significant impact of the
pattern of chiral symmetry breaking : in particular large differences can occur
between the chiral limits of two and three massless flavours (i.e., whether
$m_s$ is kept at its physical value or sent to zero). We recall some
indications of such a scenario in QCD, in relation with the peculiar dynamics
of the scalar sector. We explain how this could affect the convergence of
three-flavour chiral series, commonly used to extrapolate the results of
lattice simulations. Finally, we indicate how lattice simulations with three
dynamical flavours could unveil such an effect through the quark-mass
dependence of light meson masses and decay constants.
