The tawny nurse shark may be one of the few fishes specializing in preying on octopus . Other known food items include corals , sea urchins , crustaceans ( e.g. crabs and lobsters ) , squid , small fishes ( e.g. surgeonfish , queenfish , and rabbitfish ) , and the occasional sea snake . Hunting tawny nurse sharks swim slowly just above the sea floor , poking their heads into depressions and holes . When a prey item is found , the shark forcefully expand its large , muscular pharynx , creating a powerful negative pressure that suck the prey into its mouth .