Plants that need water or are injured may audibly "cry," according to new research. Tel-Aviv University's Lilach Hadany and colleagues determined that thirsty or recently-cut plants produce ultrasonic clicking noises. The sounds are quite high-pitched and most likely only heard by some animals—bats and mice, for example—that are close by. From Nature:
If the sounds are pitched down and sped up, "it is a bit like popcorn — very short clicks", Hadany says. "It is not singing." (Hear it in the below video.)
[…] Plants do not have vocal cords or lungs. Hadany says the current theory for how plants make noises centers on their xylem, the tubes that transport water and nutrients from their roots to their stems and leaves. Water in the the xylem is held together by surface tension, just like water sucked through a drinking straw. When an air bubble forms or breaks in the xylem, it might make a little popping noise; bubble formation is more likely during drought stress. But the exact mechanism requires further study, Hadany says.