Little snail asks mother: why do we from birth, must shoulder the hard and heavy shell?Mom: because our body without the skeletal support, can only climb, and climb unpleasant. So the protection of the shell!The little snail: caterpillar sister have no bones, also climb unhappy, why she did not back the hard and heavy shell?Mom: because caterpillar sister can become a butterfly, the sky will protect her ah.The little snail: but the earthworm younger brother didn't also bone climb unhappy, also won't become a butterfly he what don't carry this hard and heavy shell?Mom: because the earthworm younger brother will drill the earth, the earth will protect him ah.The little snail crying: we pity, the sky is not protection, don't protect the earth.Snail mother comforted him: \"so we have the shell ah!\" We don't rely on, but also the place, we are on your own.