While most animals need a specific backdrop for their camouflage to work, a few are so well-disguised they're incognito almost anywhere. Stick insects are a good example, with twig-like bodies that let them become virtually invisible just by holding still.
A wide variety of stick insects exist around the world, ranging in size from half an inch to two feet long. Often colored brown or green, they tend to freeze when threatened, sometimes swaying to mimic a branch blowing in the wind. That's not to say they can't be assertive, though — the American stick insect, for example, can spray a mild acid from two glands in its thorax to thwart would-be predators. If it gets in your eyes, it can burn and even cause temporary blindness.