Mimosa pudica, also known as bashfulgrass, touch me not, the sensitive plant, and the zombie plant: the compound leaves fold inward and droop when touched or shaken, defending themselves from harm, and re-open about half an hour later.
Click here to see a video of the leaves folding when touched, and then re-opening in time lapse. (These responses, which are exhibited by other plants too, are called seismonic movements.)
You can actually grow zombie plants in your yard and have zombie ground cover! They make decent house plants, as well, although they are more likely to produce their little puff-ball flowers when planted outdoors.
These plants are considered poisonous.