The disciples had the facts right. They remembered both miracles down to the number of baskets. What they had not done was put the facts together: if Jesus could feed thousands from a few loaves, then one loaf was no problem, and His warning about leaven could not have been about bread.

Gill says that to take His words about bread so literally "argues great want both of understanding and faith." Matthew Henry pictures Jesus saying, "As if he that multiplied five loaves, and seven, could not multiply one." It is the last of the questions Jesus asks in Mark 8:17-21, and it gathers them all up.

Mark records no answer. The question is left hanging, and the story moves to Bethsaida, where Jesus heals a blind man in two stages (Mark 8:22-26). Matthew's account finishes the scene: Jesus explains that He spoke "not ... concerning bread," and "Then understood they how that he bade them not beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees" (Matthew 16:11-12).

The KJV and ESV read differently here because they follow different Greek texts. The Textus Receptus, the Greek text behind the KJV, reads pos ou suniete, "How do you not understand?" Other Greek editions read oupo suniete, "Do you not yet understand?", which the ESV follows. Either way, Jesus is asking about understanding, not memory.

The verb suniemi means to put together or comprehend. It is the same verb Jesus used in Mark 8:17 ("neither understand"). The disciples had the pieces. They had not put them together.

Mark ends this scene with a question instead of an answer, and that is part of the message. The reader is left asking the same thing: do I understand who Jesus is from what He has done?

Mark answers it with what comes next. A blind man at Bethsaida first sees "men as trees, walking," and then sees "every man clearly" (Mark 8:24-25). Matthew Henry reads that gradual cure as a picture of how grace heals those "who by nature are spiritually blind." Then on the road to Caesarea Philippi, Peter says, "Thou art the Christ" (Mark 8:29). Jesus' patience with slow disciples is part of how He opens their eyes.