Zoom-in in the central region of the Cold Keplerian Disk simulation with weak drag (K=0.01) and low dust-to-gas ratio (δ=0.01). The left half shows the last snapshot of a run without diffusion. The lack of a restoring force causes strong clumping of dust density, which leads to a code crash very early into the simulation. The addition of diffusion, as shown in the right half of the figure, dissipates these clumps and makes the code more stable.