The swamp toad is a small creature with removable legs. If you choose to remove them, toad's legs appear in your inventory in place of the swamp toad. The text "You pull the legs off the toad. Poor toad. At least they'll grow back." appears in the chat box.
Toad's legs are used as the tertiary ingredient for agility potions and in various Gnome cooking dishes.
Swamp toads spawn in the Tree Gnome Stronghold swamp (18 spawns). 3 spawns can also be found south of Taverley east of the Taverley dungeon. Jump the Falador western wall, and go north if picking them up there.