  The effect of isospin breaking pion s-wave rescattering is included in
elastic NN scattering at low energies using effective field theory. Although
this mechanism gave a large contribution to charge symmetry breaking in np -->
d pi0, the effect is rather small in pp vs. nn scattering parameters and in the
3H-3He binding energy difference. This smallness is caused by large
cancellation of the up-down quark mass difference contribution and
electromagnetic effects to the np mass difference.
