谁能看懂一个英语笑话的含义

谁能看懂一个英语笑话的含义
看得懂内容,但实在不懂它的可笑之处啊.There was once a snail who was sick and tired of his reputation for being so slow.He decided to get some fast wheels to make up the difference.After shopping around a while,he decided that the Datson 240-Z was the car to get.So the snail goes to the nearest Datsun dealer and says he wants to buy the 240-Z,but he wants it repainted "240-S".The dealer asks,"Why 'S'?" The snail replies,"'S' stands for snail.I want everybody who sees me roaring past to know who's driving." Well,the dealer doesn't want to lose the unique opportunity to sell a car to a snail,so he agrees to have the car repainted for a small fee.The snail gets his new car and spent the rest of his days roaring happily down the highway at top speed.And whenever anyone would see him zooming by,they'd say "Wow!Look at that S-car go!"