The effects of polymer bridging on the rheological properties of silica suspensions were studied by the use of a coaxial cylinder rheometer. The apparent viscosity irreversibly increases with shearing time at shear rates beyond a certain value. This may be due to the flocculation by shear-induced bridging in which the floc-floc bond is formed by adsorption of a polymer chain extending from one particle to a particle in the other floc during collision. The critical shear rate for shear-induced bridging flocculation decreases with increasing electrolyte concentration because the energy barrier is decreased by the compression of the electrical double layer. The suspensions become elastic pastes after the bridging flocculation. The appearance of elasticity suggests the existence of a three-dimensional network of silica particles, so that the flocculation process has a critical point above which unbounded flocs of infinite size are formed. The percolation theory is applied to the elasticity threshold. The critical volume fraction of the dispersed phase for elastic responses is comparable to the critical percolation probability for the site problem on a simple cubic lattice. The shear-induced bridging process can be explained by the bond percolation concept.