In this talk I will address several problems related to B , D and Lambda_b weak decay into three final hadrons where several resonances are clearly seen. Some of them are peculiar and do not correspond to ordinary mesons and baryons, of q qbar or qqq nature, but they are more complex structures, like the f0(980),a0(980), kappa(800) and Lambda(1405). I will show how to interpret the experimental results, mostly from LCHb, with elements of the chiral unitary approach, and how these experiments offer a new insight on the structure of these hadrons. I will address the Lambda_b -> J/psi K- p decay from this perspective, done before the LHCb experiment, where a contribution from the Lambda(1405) was predicted, and compare with the results of the experiment. I will also show results for a baryon of hidden charm predicted before the experiment and then our interpretation of the pentaquark signals seen in the experiment.