  We give an overview of a model to describe deep-inelastic scattering (DIS)
off the deuteron with a spectator proton, based on the virtual nucleon
approximation (VNA). The model accounts for the final-state interactions (FSI)
of the DIS debris with the spectator proton. Values of the rescattering cross
section are obtained by fits to high-momentum spectator data. By using the
so-called "pole extrapolation method", free neutron structure functions can be
obtained by extrapolating low-momentum spectator proton data to the on-shell
neutron pole. We apply this method to the BONuS data set and find a surprising
Bjorken $x$ dependence, indicating a possible rise of the neutron to proton
structure function ratio at high $x$.
