'Beware of the Leaven' in the Bible

And Jesus said to them, “Watch out and beware of the leaven of the Pharisees and Sadducees.”

How is it that you do not understand that I did not speak to you concerning bread? But beware of the leaven of the Pharisees and Sadducees.”

Then they understood that He did not say to beware of the leaven of bread, but of the teaching of the Pharisees and Sadducees.