  We study Brownian motion in a space with a high density of moving obstacles
in 1, 2 and 3 dimensions. Our tracers diffuse anomalously over many decades in
time, before reaching a diffusive steady state with an effective diffusion
constant $D_\mathrm{eff}$ that depends on the obstacle density and diffusivity.
The scaling of $D_\mathrm{eff}$, above and below a critical regime at the
percolation point for void space, is characterized by two critical exponents:
the conductivity $\mu$, also found in models with frozen obstacles, and $\psi$,
which quantifies the effect of obstacle diffusivity.
