|Click to enlarge|
The pictures to the right are before and after a light touch. The action takes place in less than a second. Cleverly called "rapid plant movement", it is a property of several plants in the Mimosa family. The Venus Flytrap's capture of insects is another example of rapid plant movement. Also some plants are able to flip out pollen with their petals at half the speed of sound!
|One second later|
Wikipedia. You can watch the leaves fold up in a short video of another Mimosa species.