12:1 thousands. The word strictly means “ten thousands” but was used generally of any large number. Jesus’ teaching was addressed primarily to His disciples, though the crowds would also have heard and profited.
leaven. People were familiar with the way a little leaven slowly permeates and transforms a large mass of dough. Jesus elsewhere uses the figure of leaven to illustrate the hidden working of God’s kingdom (13:21), but here it describes the negative influence of the Pharisees (Mark 8:15 note).