  YFeO$_3$ and LaFeO$_3$ are members of the rare-earth orthoferrites family
with \textit{Pbnm} space group. Using inelastic neutron scattering, the
low-energy spin excitations have been measured around magnetic Brillouin zone
center. Splitting of magnon branches and non-zero magnon gap is observed for
both compounds, which is similar to the behavior observed in multiferroic
BiFeO$_3$. Spin wave calculations which include both Dzyaloshinsky-Moriya
interactions and single-ion anisotropy in the spin-Hamiltonian comprehensively
accounts for all the experimentally observed features. Our results offer
insight into the unifying physics underlying the Fe$^{3+}$-based perovskites as
well as their distinguishing characteristics.
