Mimosa pudica
The leaves also close when touched, warmed, blown, or shaken. When the plant is disturbed, specific regions on the stems release potassium ions which force water out of the cell vacuoles. The water diffuses out of the cells, producing a loss of cell pressure and cell collapse; this differential turgidity between different regions of cells results in the closing of the leaflets and the collapse of the leaf petiole. This is quite a common trait in the Mimosoideae subfamily of the legume family, Fabaceae. The stimulus can also be transmitted to neighbouring leaves.  The function of this trait is not known. The plant may use its ability as a defense from predators. Animals may be afraid of a fast moving plant and would rather eat a less active one.  Another possible explanation is that the sudden movement dislodges harmful insects.