Geckos

The Australian spiny-tailed gecko (Diplodactylus williamsi) displays the most unique defense of all lizards. When this grey, inconspicuous gecko suddenly swings opens its jaws, it displays a vivid, dark purple mouth outlined in bright blue. It may also emit a high-pitched squeak and, if attacked, shoots a thick, gooey liquid from spiny knobs on its tail, covering its enemy with a sticky weblike substance.

Although geckos in general show aggressive displays such as arching the back, stiffening the limbs to increase their height, and wagging their tails, they are relatively nonaggressive, fighting among themselves only when defending a homesite or feeding territory from a determined invader. Although small geckos will attack a foe many times their size if threatened. The Australian barking gecko (Underwoodisaurus milii) barks and lunges even at humans. Very few species of gecko are strong enough to break the human skin, and none are poisonous.