a boundary is a mean of old / child toad
pelophryne is toad. tree_toad is frog. bleeding_toad is amphibian. european_toad is true_toad. toad is anura. western_narrow_mouthed_toad is frog. fire_bellied_toad is toad. mongolian_toad is toad. duttaphrynus is toad. rococo_toad is toad.