chameleons change their colours to blend in with the surrounding environment. crabs scuttle sideways to get to/avoid something in their path. puffer fish swell up to volleyball size proportions.
contrary to popular belief, ostriches do not bury their heads in the sand. the closest they get is to lay their long necks flat on the ground so that they become less visible, i would imagine the human version of this is the small child who rolls up into a ball in the corner and covers their face- if i cant see you, then you cant see me. ostriches also have those powerful legs; great to run away from any situation!