  We discuss the importance of the background in order to understand the
scattering in the J^{PC}=0^{++} low and intermediate energy region and in
particular regarding the \sigma meson. In order to appreciate better its
importance we compare with the \rho meson in the P-wave \pi\pi scattering. We
also point out that in present analyses of three-body heavy meson decays, like
those of D^+ and B, the role of this background is still not properly settled
although it happens to be considerably smaller.
