Some bacteria use type IV pili to move along surfaces within a biofilm. (Biofilms are to viscous for bacteria to swim through with flagella.) A bacterium sitting at location "X" extends and anchors its pili. As the pili contract, the pili become stretched or taut. As the anchoring pilus on the right detaches, the taut pili "slingshot" the bacterium to the left. This motion alternates with the twitching motility (see Fig. 5) also caused by type IV pili and enables a more rapid motion and direction change than with the twitching motility because the rapid slingshotting motion reduces the viscosity of the surrounding biofilm.