We never thought to test this method on flora until one of my postdoctoral fellows, Corinne Lee-Kubli, received a touch-me-not plant as a gift. As a defense mechanism, its leaves fold inward when stroked or shaken. Given this ability to move in response to mechanical force, I thought it might also react in a similar way to the physical vibrations coming from sound waves. We dipped a branch in ultrasound jelly, the same kind doctors use on people, and placed it on the probe. As we predicted, the leaves folded when the waves reached them.