A mimosa is a shrub. It is native to tropical America. It has fern-like leaflets. When threatened, the leaves of the mimosa close up on themselves. The greater the threat seems, the faster they will close. A light touch might spark a slow response. A hard flick might make an entire plant's leaves close quickly. An electrical signal moves down the stem. The distance along the plant that the response spreads also depends upon the stimulus. At the base of each leaflet, the signal tells the leaflet to close. It works the same way nerve cells work.
