Whoa...now these are some really cool plants!
They are called Touch-Me-Nots, the scientific name is Mimosa Pudica which is derived from the Latin word for shy.
At just the slightest touch the leaves of the plant fold inward and drop down.
Scientists believe that the plant evolved this way to trick leaf-eating animals into believing it wasn't actually a plant.
It's nice to meet a small weed with so much personality!