Out of curiousity (and I do NOT want to start a Bible war here since I'm WAY out of my league), what version of the Bible are you using? That quote seems extremely different from mine (King James Version):
And Jesus said, "Are ye also yet without understanding?"
Of course it is within the context of a larger story, but what strikes me is how the translation has gone from asking if they yet understand to asking if they are "dull". Seems to me that accusing someone of being "dull" is akin to calling them 'mentally slow' or stupid. I don't think that was the intent of his statement.
Anyway, just curious.
Matthew 15:10-20 (New International Version)
10Jesus called the crowd to him and said, "Listen and understand. 11What goes into a man's mouth does not make him 'unclean,' but what comes out of his mouth, that is what makes him 'unclean.' "
12Then the disciples came to him and asked, "Do you know that the Pharisees were offended when they heard this?"
13He replied, "Every plant that my heavenly Father has not planted will be pulled up by the roots. 14Leave them; they are blind guides. If a blind man leads a blind man, both will fall into a pit."
15Peter said, "Explain the parable to us."
16"Are you still so dull?" Jesus asked them. 17"Don't you see that whatever enters the mouth goes into the stomach and then out of the body? 18But the things that come out of the mouth come from the heart, and these make a man 'unclean.' 19For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false testimony, slander. 20These are what make a man 'unclean'; but eating with unwashed hands does not make him 'unclean.' "