“How could you fail

To perceive

That I was not speaking

To you

About bread?

Beware of the yeast

Of the Pharisees

And Sadducees!’

Then they understood

That he had not told them

To beware

Of the yeast of the bread,

But of the teaching

Of the Pharisees

And Sadducees.”

πῶς οὐ νοεῖτε ὅτι οὐ περὶ ἄρτων εἶπον ὑμῖν; προσέχετε δὲ ἀπὸ τῆς ζύμης τῶν Φαρισαίων καὶ Σαδδουκαίων.

τότε συνῆκαν ὅτι οὐκ εἶπεν προσέχειν ἀπὸ τῆς ζύμης τῶν ἄρτων, ἀλλὰ ἀπὸ τῆς διδαχῆς τῶν Φαρισαίων καὶ Σαδδουκαίων.

This is unique to Matthew.  Jesus, via Matthew, asked the disciples how they could not perceive or understand (πῶς οὐ νοεῖτε) that he was not speaking to them about bread (ὅτι οὐ περὶ ἄρτων εἶπον ὑμῖν).  Instead, he was warning them about the yeast of the Pharisees and Sadducees (προσέχετε δὲ ἀπὸ τῆς ζύμης τῶν Φαρισαίων καὶ Σαδδουκαίων).  Finally, they understood (τότε συνῆκαν) that he was not talking to them about the yeast in bread (ὅτι οὐκ εἶπεν προσέχειν ἀπὸ τῆς ζύμης τῶν ἄρτων), but the yeast of the teachings of the Pharisees and Sadducees (ἀλλὰ ἀπὸ τῆς διδαχῆς τῶν Φαρισαίων καὶ Σαδδουκαίων.).  Once again, Jesus, via Matthew, took a shot at both the Pharisees and Sadducees, but not the Scribes.  The Pharisees were a political party, a social movement, and a religious school of thought that followed the Law of Moses, but with a number of oral traditions.  They had they own expert explanations of Jewish law that sometimes appeared to be hypocritical or arrogant, with a form of Judaism that extended beyond the Temple.  The Sadducees, on the other hand, were generally aristocratic priestly officials, tied to the Temple and ritual purifications.  They were less concerned about oral traditions, so that they might have been political religious rivals to the Pharisees.  However, Jesus warned his disciples against both groups and their teaching yeasts.