Gerbils are mainly sandy-colored, so they blend in well with the Mongolian desert. But the rodent has a tuft of dark hair on its tail. If a predator, such as a fox, spots the creature moving, it will attack the dark tail end, which is easier to see than the head. If the fox manages to grab the gerbil's tail it can break off, giving the animal a chance to escape, though its tail will not grow again.