We all cry for water when we are thirsty. But do you know, in very hot, dry weather, plants also make very low sounds as if they are crying for help?

    You see, in a plant's stem there are several hundred "water pipes" that bring water from soil all the way up to the leaves. When the ground turns dry, it becomes harder and harder for plants to do this.

    On very hot days, plants have to get any water that they can get.

    Scientist Robot Winter has found out that when plants can get no water, their "water pipes" snap(发出声音). When that happens, the whole plant vibrates(振动) a little.

    Robot knows that healthy, well-watered plants are quiet.  He also knows that dry plants are many insects' "favourite" and they often attack(袭击) them. How do the insects know which are healthy plants and which are not? Robot thinks that the insects may hear the plants "crying" and they may come to kill them.