Rashi: It is the stick of the plowshare. Radak - at one end is a needle. One who plows stings the ox with it. It is called Malmad, for it is as if it is Melamed (teaches) the ox to plow. Yonason translates bi'Frash Toraya. Due to this, people who ride on horses are called Parashim (Nachum 3:3), for they sting [the horse, to make it go faster] with Perishin (spikes) on their feet (in back of their boots).