Which of these is the most striking feature of Darwin's frog?

Darwin's frog (Rhinoderma darwinii), also called the southern Darwin's frog is a rhinodermatid frog native to the forest streams of Chile and Argentina. It was first described by the French zoologist André Marie Constant Duméril and his assistant Gabriel Bibron in 1841, and is named after Charles Darwin, who had previously discovered it in Chile during his world voyage on HMS Beagle.

The most striking feature of this frog is the tadpoles' development inside the vocal sac of the male.

Darwin's frog feeds on insects and other arthropods. It not only has to hunt, but also needs to hide from its predators. It relies on camouflage to avoid predators, lying on the ground looking like a dead leaf until the predator passes by. Another defensive position is turning on the back and exposing the boldly patterned ventral surface.

The female Darwin's frog lays up to forty eggs among the leaf litter. The male guards them for about three to four weeks until the developing embryos begin to move, and then he ingests the eggs and holds them in his vocal sac. They hatch about three days later and he continues to carry the tadpoles around in his vocal sac where they feed off their egg yolks and secretions produced by the wall of the sac until metamorphosis. At this stage, about 6 weeks after being swallowed (a duration in which the adult male eats nothing), the small frogs hop out of the male's mouth and disperse.