  We have studied the effect of small amounts of added liquid on the dynamic
behavior of a granular system consisting of spherical glass beads. The critical
acceleration $\Gamma$ for fluidization is found to increase strongly when
liquid is added. It furthermore depends on the bead radius, the height of the
sample, and the shaking frequency. As our main result, we find that these
dependencies can be presented in a factorized form. We present a simple model
which accounts for most of our findings.
