  We study the percolation velocity, $v_p,$ of a fine spherical particle in a
sheared large-particle bed under gravity using discrete element method
simulations for large-to-fine particle diameter ratios, $R=d/d_f,$ below and
above the free-sifting threshold, $R_t\approx6.5.$ For $R<R_t,$ $v_p$ initially
increases with increasing shear rate, $\dot\gamma,$ as shear-driven bed
rearrangement reduces fine-particle trapping but then decreases toward zero due
to fine-particle excitation for $\dot\gamma\sqrt{d/g}\gtrsim 0.1$. For $R>R_t$,
$v_p$ is constant at low $\dot\gamma$ but decreases toward zero at higher shear
rates due to fine-particle excitation.
