[al:新概念英语（四）] [ar:MP3 同步字幕版（英音）] [ti:Porpoises] [by:更多学习内容，请到chazidian.com搜索“新概念”] [00:01.49]Lesson 18 [00:03.31]Porpoises [00:10.62]What would you say is the main characteristic of porpoises? [00:17.06]There has long been a superstition among mariners that porpoises will save drowning men by pushing them to the surface, [00:25.54]or protect them from sharks by surrounding them in defensive formation. [00:31.72]Marine Studio biologists have pointed out that, however intelligent they may be, it is probably a mistake to credit dolphins with any motive of life-saving. [00:43.54]On the occasions when they have pushed to shore an unconscious human being they have much more likely done it out of curiosity or for sport, [00:53.55]as in riding the bow waves of a ship. [00:57.55]In 1928 some porpoises were photographed working like beavers to push ashore a waterlogged mattress. [01:06.19]If, as has been reported, they have protected humans from sharks, [01:11.15]it may have been because curiosity attracted them and because the scent of a possible meal attracted the sharks. [01:18.95]Porpoises and sharks are natural enemies. [01:22.48]It is possible that upon such an occasion a battle ensued, with the sharks being driven away or killed. [01:31.19]Whether it be bird, fish or beast, the porpoise is intrigued with anything that is alive. [01:38.09]They are constantly after the turtles, who peacefully submit to all sorts of indignities. [01:44.87]One young calf especially enjoyed raising a turtle to the surface with his snout, and then shoving him across the tank like an aquaplane. [01:54.64]Almost any day a young porpoises may be seen trying to turn a 300-pound sea turtle over by sticking his snout under the edge of his shell [02:04.07]and pushing up for dear life. [02:06.72]This is not easy, and may require two porpoises working together. [02:12.26]In another game, as the turtle swims across the oceanarium, the first porpoise swoops down from above and butts his shell with his belly. [02:22.62]This knocks the turtle down several feet. [02:25.63]He no sooner recovers his equilibrium than the next porpoises comes along and hits him another crack. [02:32.79]Eventually the turtle has been butted all the way down to the floor of the tank. [02:38.16]He is now satisfied merely to try to stand up, but as soon as he does so a porpoise knocks him flat. [02:46.00]The turtle at last gives up by pulling his feet under his shell and the game is over.