  Recent results on Dalitz analysis of three-pseudoscalar decays are discussed
in the context of probing charm hadronic-decay mechanisms: the role of FSI
effects, which create phase shifts between the interfering resonant channels,
can be studied in the different decay modes and the annihilation contribution
measured in the charm sector through the $D^+_s \to \pi^+\pi^-\pi^+$ decay.
