Matthew 16:12
Then they understood that He was not telling them to watch out for the yeast in [physical] bread, but for the teaching of the Pharisees and Sadducees.
Matthew 26:26
And as they were eating, Jesus took a [small] loaf of bread, asked God's blessing on it, then broke it and gave pieces to His disciples and said, "Take some and eat it; this is [i.e., represents] my [physical] body."
John 6:52-57
Then the Jews [who were assembled in the synagogue. See verse 59] began arguing bitterly with one another, saying, "How can this man give us his physical body to eat?"
1 Corinthians 5:6-8
Your boasting is not good. Do you not know that a little yeast can leaven the whole batch of dough?
Galatians 5:9
A little bit of yeast permeates the whole batch of dough [i.e., a few people can influence everyone else to do the wrong thing in this matter].
1 Thessalonians 1:6
And you became imitators of us and of the Lord. [And even though] you suffered much affliction, you welcomed the message with joy [given to you] by the Holy Spirit,