  The mechanism of a rogue water wave is still unknown. One popular conjecture
is that the Peregrine wave solution of the nonlinear Schr\"odinger equation
(NLS) provides a mechanism. A Peregrine wave solution can be obtained by taking
the infinite spatial period limit to the homoclinic solutions. In this article,
from the perspective of the phase space structure of these homoclinic orbits in
the infinite dimensional phase space where the NLS defines a dynamical system,
we exam the observability of these homoclinic orbits (and their
approximations). Our conclusion is that these approximate homoclinic orbits are
the most observable solutions,and they should correspond to the most common
deep ocean waves rather than the rare rogue waves. We also discuss other
possibilities for the mechanism of a rogue wave: rough dependence on initial
data or finite time blow up.
