Stonefish are sluggish, bottom-dwelling fish that live among rocks or coral and in mud flats and estuaries. Thickset fish with large heads and mouths, small eyes, and bumpy skins covered with wartlike lumps and, sometimes, fleshy flaps, they rest on the bottom, unmoving, blending almost exactly with their surroundings in form and colour. They are dangerous fish. Difficult to see, they can, when stepped on, inject quantities of venom through grooves in their dorsal-fin spines. Wounds produced by these fish are intensely painful and sometimes fatal.