  The two-orbital J1-J2 model that describes a square lattice of frustrated
spin-1 iron atoms is analyzed within the linear spin-wave approximation and by
exact diagonalization over a 4x4 cluster. A quantum critical point (QCP) is
identified that separates hidden magnetic order at weak Hund's rule coupling
from a commensurate spins density wave (cSDW) at strong Hund's rule coupling.
Although the moment for cSDW order is small at the QCP, the critical linear
spin-wave spectrum shows strong low-energy excitations centered at the
wavenumbers that correspond to cSDW order. These disperse anisotropically. A
fit to the magnetic excitation spectrum of ferro-pnictide materials obtained
recently by inelastic neutron scattering measurements notably accounts for the
absence of softening at the wavenumber that corresponds to Neel order.
