  Hydrodynamic models of RR Lyrae pulsation display a very rich behaviour.
Contrary to earlier expectations, high order resonances play a crucial role in
the nonlinear dynamics representing the interacting modes. Chaotic attractors
can be found at different time scales: both in the pulsation itself and in the
amplitude equations shaping the possible modulation of the oscillations.
Although there is no one-to-one connection between the nonlinear features found
in the numerical models and the observed behaviour, the richness of the found
phenomena suggests that the interaction of modes should be taken seriously in
the study of the still unsolved puzzle of Blazhko effect. One of the main
lessons of this complex system is that we should rethink the simple
interpretation of the observed effect of resonances.
