Mat 16:6 Take heed and beware of the leaven of the Pharisees and of the Sadducees.

This statement confuses the apostles, but it is perfectly consistent with Christ's uses of symbols. For Christ, "bread" symbolizes the physical body, but "leaven" is the spirit that motivates the body. In his previous verse, Christ uses the Jonah analogy (another symbol for the physical world) to say that all the Pharisees and Sadducees will ever accept is physical proof. He here is warning his followers in terms that translate as relating purely to the physical world not to be infected by this spirit of materialism.

A most accurate translation: See and pay attention to the leaven of the Pharisee and Sadducees.
A symbolic translation: Look and behold the physical spirit of the priests and authorities.

"Take heed" is from horaô, which means "to see with the eyes," "to look," and "to observe."

"Beware" is from prosechô, which means "to hold to," "to offer," "to turn toward a thing," and "to pay attention." Only in the NT is it ever translated as "beware."