  Canard cascading (CC) is observed in dynamical networks with global adaptive
coupling. It is a fast-slow phenomenon characterized by a recurrent sequence of
fast transitions between distinct and slowly evolving quasi-stationary states.
In this letter, we uncover the dynamical mechanisms behind CC, using an
illustrative example of globally and adaptively coupled semiconductor lasers,
where CC represents sequential switching on and off the lasers. Firstly, we
show that CC is a robust and truly adaptive network effect that is scalable
with network size and does not occur without adaptation. Secondly, we uncover
multiple saddle slow manifolds (unstable quasi-stationary states) linked by
heteroclinic orbits (fast transitions) in the phase space of the system. This
allows us to identify CC with a novel heteroclinic canard orbit that organises
different unstable quasi-stationary states into an intricate fast-slow limit
cycle. Although individual quasi-stationary states are unstable (saddles), the
CC cycle as a whole is attractive and robust to parameter changes.
