Cover yourself in spines, spikes, quills, exhale an intolerable odor, inject poison with a quill or stinger. When things get rough, flee, hide, freeze, take on the colors of the surrounding leaves, put on a thick, scaly shell, pull in your head, puff out your cheeks, bristle your hair, turn red, look mean. Confuse your enemies with spots, stun them through hypnotism, trick them with another species' song. Anything's fair if it aids survival. Beyond my little morning excretions, I throw out a few words, a few spots, a few tunes; I build a rampart enclosing my territory, a wall, my little wall of China.
Van Gulik tells us that the ancient Chinese built little walls in front of their houses to trip up the ghosts that wander at night and attack the living. He claims that such ghosts only know how to walk in a straight line. It's their weak point and gives them away every time.