  We investigate the interaction of two pulses (pump and probe) scattered by a
nonlinear epsilon-near-zero (ENZ) slab whose thickness is comparable with the
ENZ wavelength. We show that when the probe has a narrow spectrum localized
around the ENZ wavelength its transmission is dramatically affected by the
intensity of the pump. Conversely, if the probe is not in the ENZ regime, its
propagation is not noticeably affected by the pump. Such all-optical modulation
is due to the oversensitive character of the ENZ regime and it is so efficient
to even occur in a wavelength thick slab.
