Fig. 1. Cockroaches (B. discoidalis) were run over a rough terrain (A) with a Gaussian distribution of surface heights (B) up to three times the hip height of the animal (C). The cockroach experienced repeated random perturbation while negotiating the terrain. Offsetting the terrain from the entry and exit tracks resulted in very large (4–6 times hip height) perturbations to the first and last steps on the terrain. The level surface of all blocks was 1 cmx1 cm.