In Mark 8:17, Jesus asks the disciples if their hearts are hardened — the specific accusation leading to this conclusion.

In Mark 8:12, Jesus rebukes the Pharisees for demanding a sign — reflecting the same spiritual dullness he addresses here.

In Mark 6:52, the disciples did not understand about the loaves and their hearts were hardened — the same failure rebuked here.

In Matthew 16:11, the same event is recorded with Jesus clarifying he spoke about the leaven of the Pharisees.

In Matthew 16:12, the disciples finally understand — contrasting their lack of understanding here.