稍察觉有烈日的迹象,蜗牛就将它的身体纳入其外壳并用薄盖关闭开口.
at the least sign of
意思是：稍微有.的迹象（征兆）
draw into
在这里是吸入,纳入的意思.此外它还开进,驶入的意思.
All these activists must be drawn into the work.
所有这些积极分子都应吸取来参加这项工作.
Dirt and dust are draw into a vacuum cleaner by suction.
污物和灰尘被吸入吸尘器.
That is to say, draw air into your abdomen rather than stomach.
也就是吸气的时候让气流下沉,吸进自己的腹部.而不是吸进胃部或者胸部.