鈍頭蛇是一個特殊的族群，牠們以蝸牛為主食，因為絕大多數蝸牛，螺殼都是順時鐘方向旋轉的右旋型，為了更有效率的取食右旋型蝸牛，牠們演化成右撇子型的掠食者；有趣的是，因為右撇子天敵的選汰壓力，突變產生的左旋型蝸牛存活率增高，於是演化出了左旋型的蝸牛種類，這部影片述說蝸牛與鈍頭蛇兩者間有趣的互動。

The slug snake is a special genus of snakes. They feed on snails. Most snails have dextral shells, which means that the shells coil to the right. Therefore, the slug snake evolved mouths that can bite through dextral shells and eat the snails. What’s interesting, though, is that because of this, more snails with sinistral, or left-coiling, shells have survived, and a new species of left-coiling shelled snails evolved.

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