From above, Bombina orientalis is mottled green and black and disappears against pondweed. The warning colour is entirely on the ventral surface, which is useless as a signal until the animal chooses to show it. Threatened, the toad performs the unken reflex, named from the German Unke for these toads: it arches the back sharply, raises the fore and hind limbs over the body, and turns the palms and belly upward.
The display is backed by chemistry. Skin glands release bombesin and related peptides along with bombinatoxin, producing a bitter, irritating secretion that most predators reject. The pairing of a hidden warning colour with a genuine defence is aposematism used on demand rather than advertised continuously, which preserves camouflage while resting.
The reflex is not confined to this species. Fire-bellied toads across the genus Bombina and several unrelated salamanders adopt comparable postures to reveal bright ventral colouring, which makes the unken reflex a convergent behaviour rather than a family trait.