  This paper concerns the interaction between non-axisymmetric inertial waves
and their corotation resonances in a hydrodynamical disk. Inertial waves are of
interest because they can localise in resonant cavities circumscribed by
Lindblad radii, and as a consequence exhibit discrete oscillation frequencies
that may be observed. It is often hypothesised that these trapped eigenmodes
are affiliated with the poorly understood QPO phenomenon. We demonstrate that a
large class of non-axisymmetric 3D inertial waves cannot manifest as trapped
normal modes. This class includes any inertial wave whose resonant cavity
contains a corotation singularity. Instead, these `singular' modes constitute a
continuous spectrum and, as an ensemble, are convected with the flow, giving
rise to shearing waves. Lastly, we present a simple demonstration of how the
corotation singularity stabilizes three-dimensional perturbations in a slender
torus.
