There has long been a superstition among mariners（水手） that porpoises（海豚） will save drowning（淹死） men by pushing them to the surface, or protect them from sharks by surrounding（围绕） them in defensive（自卫的） formation（形成）. Marine（海运业） studio biologists（生物学家） have pointed out that however intelligent they may be, it is probably a mistake to credit dolphins with any motive（动机） of life-saving（储蓄）. On the occasions when they have pushed to shore an unconscious（无意识的） human being, they have much more likely done it out of curiosity（好奇） or for sport, as in riding the bow（弓） waves of a ship. In 1928 some porpoises were photographed working like beavers to push ashore（在岸上） a waterlogged mattress. If, as has been reported, they have protected humans from sharks, it may have been because curiosity attracted them and because the scent（气味） of a possible meal attracted the sharks.