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(Bombina), small amphibian (family Bombinatoridae) characterized by bright orange markings on the undersides of its grayish body and limbs. The common fire-bellied toad (B. bombina) is a pond dweller about 5 centimetres (2 inches) long. When disturbed it raises its forearms and arches its head and hind legs over its back. Resting on the lower part of its tautly curved abdomen, it freezes with the bright colours of its underside on display. This reaction to danger, the "unken reflex," is thought to be a warning signal to indicate to potential predators that the skin of the frog is poisonous