Different susceptibility expansions for the polarization densityPare compared to identify cascading contributions to the nonlinear response of a medium. In certain liquids pair-correlation dependence of the nonlinear optical susceptibilities has been observed. To isolate the cascading effects that depend most sensitively on pair correlation and near-field effects, a simple statistical model forPis applied to the case of a liquid whose oriented molecules have only first hyperpolarizabilities; then all third-order effects inPare a consequence of cascading.