 Food is mostly selected by sight , even in conditions of dim light . Movement of the prey triggers a feeding response . Frogs have been caught on fish hooks baited with red flannel and green frogs ( Rana clamitans ) have been found with stomachs full of elm seeds that they had seen floating past . Toads , salamanders and caecilians also use smell to detect prey . This response is mostly secondary because salamanders have been observed to remain stationary near odoriferous prey but only feed if it moves . Cave @-@ dwelling amphibians normally hunt by smell . Some salamanders seem to have learned to recognize immobile prey when it has no smell , even in complete darkness . 
